rfc9200.original   rfc9200.txt 
ACE Working Group L. Seitz Internet Engineering Task Force (IETF) L. Seitz
Internet-Draft Combitech Request for Comments: 9200 Combitech
Intended status: Standards Track G. Selander Category: Standards Track G. Selander
Expires: 2 March 2022 Ericsson ISSN: 2070-1721 Ericsson
E. Wahlstroem E. Wahlstroem
S. Erdtman S. Erdtman
Spotify AB Spotify AB
H. Tschofenig H. Tschofenig
Arm Ltd. Arm Ltd.
29 August 2021 March 2022
Authentication and Authorization for Constrained Environments (ACE) Authentication and Authorization for Constrained Environments (ACE)
using the OAuth 2.0 Framework (ACE-OAuth) Using the OAuth 2.0 Framework (ACE-OAuth)
draft-ietf-ace-oauth-authz-45
Abstract Abstract
This specification defines a framework for authentication and This specification defines a framework for authentication and
authorization in Internet of Things (IoT) environments called ACE- authorization in Internet of Things (IoT) environments called
OAuth. The framework is based on a set of building blocks including ACE-OAuth. The framework is based on a set of building blocks
OAuth 2.0 and the Constrained Application Protocol (CoAP), thus including OAuth 2.0 and the Constrained Application Protocol (CoAP),
transforming a well-known and widely used authorization solution into thus transforming a well-known and widely used authorization solution
a form suitable for IoT devices. Existing specifications are used into a form suitable for IoT devices. Existing specifications are
where possible, but extensions are added and profiles are defined to used where possible, but extensions are added and profiles are
better serve the IoT use cases. defined to better serve the IoT use cases.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 2 March 2022. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9200.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Overview
3.1. OAuth 2.0 . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. OAuth 2.0
3.2. CoAP . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.2. CoAP
4. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 11 4. Protocol Interactions
5. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5. Framework
5.1. Discovering Authorization Servers . . . . . . . . . . . . 16 5.1. Discovering Authorization Servers
5.2. Unauthorized Resource Request Message . . . . . . . . . . 16 5.2. Unauthorized Resource Request Message
5.3. AS Request Creation Hints . . . . . . . . . . . . . . . . 17 5.3. AS Request Creation Hints
5.3.1. The Client-Nonce Parameter . . . . . . . . . . . . . 19 5.3.1. The Client-Nonce Parameter
5.4. Authorization Grants . . . . . . . . . . . . . . . . . . 20 5.4. Authorization Grants
5.5. Client Credentials . . . . . . . . . . . . . . . . . . . 20 5.5. Client Credentials
5.6. AS Authentication . . . . . . . . . . . . . . . . . . . . 21 5.6. AS Authentication
5.7. The Authorization Endpoint . . . . . . . . . . . . . . . 21 5.7. The Authorization Endpoint
5.8. The Token Endpoint . . . . . . . . . . . . . . . . . . . 21 5.8. The Token Endpoint
5.8.1. Client-to-AS Request . . . . . . . . . . . . . . . . 22 5.8.1. Client-to-AS Request
5.8.2. AS-to-Client Response . . . . . . . . . . . . . . . . 25 5.8.2. AS-to-Client Response
5.8.3. Error Response . . . . . . . . . . . . . . . . . . . 27 5.8.3. Error Response
5.8.4. Request and Response Parameters . . . . . . . . . . . 28 5.8.4. Request and Response Parameters
5.8.4.1. Grant Type . . . . . . . . . . . . . . . . . . . 28 5.8.4.1. Grant Type
5.8.4.2. Token Type . . . . . . . . . . . . . . . . . . . 29 5.8.4.2. Token Type
5.8.4.3. Profile . . . . . . . . . . . . . . . . . . . . . 29 5.8.4.3. Profile
5.8.4.4. Client-Nonce . . . . . . . . . . . . . . . . . . 30 5.8.4.4. Client-Nonce
5.8.5. Mapping Parameters to CBOR . . . . . . . . . . . . . 30 5.8.5. Mapping Parameters to CBOR
5.9. The Introspection Endpoint . . . . . . . . . . . . . . . 31 5.9. The Introspection Endpoint
5.9.1. Introspection Request . . . . . . . . . . . . . . . . 32 5.9.1. Introspection Request
5.9.2. Introspection Response . . . . . . . . . . . . . . . 33 5.9.2. Introspection Response
5.9.3. Error Response . . . . . . . . . . . . . . . . . . . 34 5.9.3. Error Response
5.9.4. Mapping Introspection Parameters to CBOR . . . . . . 35 5.9.4. Mapping Introspection Parameters to CBOR
5.10. The Access Token . . . . . . . . . . . . . . . . . . . . 36 5.10. The Access Token
5.10.1. The Authorization Information Endpoint . . . . . . . 36 5.10.1. The Authorization Information Endpoint
5.10.1.1. Verifying an Access Token . . . . . . . . . . . 38 5.10.1.1. Verifying an Access Token
5.10.1.2. Protecting the Authorization Information 5.10.1.2. Protecting the Authorization Information Endpoint
Endpoint . . . . . . . . . . . . . . . . . . . . . 39 5.10.2. Client Requests to the RS
5.10.2. Client Requests to the RS . . . . . . . . . . . . . 40 5.10.3. Token Expiration
5.10.3. Token Expiration . . . . . . . . . . . . . . . . . . 41 5.10.4. Key Expiration
5.10.4. Key Expiration . . . . . . . . . . . . . . . . . . . 42 6. Security Considerations
6. Security Considerations . . . . . . . . . . . . . . . . . . . 43 6.1. Protecting Tokens
6.1. Protecting Tokens . . . . . . . . . . . . . . . . . . . . 43 6.2. Communication Security
6.2. Communication Security . . . . . . . . . . . . . . . . . 44 6.3. Long-Term Credentials
6.3. Long-Term Credentials . . . . . . . . . . . . . . . . . . 44 6.4. Unprotected AS Request Creation Hints
6.4. Unprotected AS Request Creation Hints . . . . . . . . . . 45 6.5. Minimal Security Requirements for Communication
6.5. Minimal Security Requirements for Communication . . . . . 45 6.6. Token Freshness and Expiration
6.6. Token Freshness and Expiration . . . . . . . . . . . . . 46 6.7. Combining Profiles
6.7. Combining Profiles . . . . . . . . . . . . . . . . . . . 47 6.8. Unprotected Information
6.8. Unprotected Information . . . . . . . . . . . . . . . . . 47 6.9. Identifying Audiences
6.9. Identifying Audiences . . . . . . . . . . . . . . . . . . 48 6.10. Denial of Service Against or with Introspection
6.10. Denial of Service Against or with Introspection . . . . . 49 7. Privacy Considerations
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 49 8. IANA Considerations
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50 8.1. ACE Authorization Server Request Creation Hints
8.1. ACE Authorization Server Request Creation Hints . . . . . 50 8.2. CoRE Resource Type Registry
8.2. CoRE Resource Type Registry . . . . . . . . . . . . . . . 51 8.3. OAuth Extensions Error Registration
8.3. OAuth Extensions Error Registration . . . . . . . . . . . 51 8.4. OAuth Error Code CBOR Mappings Registry
8.4. OAuth Error Code CBOR Mappings Registry . . . . . . . . . 52 8.5. OAuth Grant Type CBOR Mappings
8.5. OAuth Grant Type CBOR Mappings . . . . . . . . . . . . . 52 8.6. OAuth Access Token Types
8.6. OAuth Access Token Types . . . . . . . . . . . . . . . . 53 8.7. OAuth Access Token Type CBOR Mappings
8.7. OAuth Access Token Type CBOR Mappings . . . . . . . . . . 53 8.7.1. Initial Registry Contents
8.7.1. Initial Registry Contents . . . . . . . . . . . . . . 53 8.8. ACE Profile Registry
8.8. ACE Profile Registry . . . . . . . . . . . . . . . . . . 54 8.9. OAuth Parameter Registration
8.9. OAuth Parameter Registration . . . . . . . . . . . . . . 54 8.10. OAuth Parameters CBOR Mappings Registry
8.10. OAuth Parameters CBOR Mappings Registry . . . . . . . . . 54 8.11. OAuth Introspection Response Parameter Registration
8.11. OAuth Introspection Response Parameter Registration . . . 55 8.12. OAuth Token Introspection Response CBOR Mappings Registry
8.12. OAuth Token Introspection Response CBOR Mappings 8.13. JSON Web Token Claims
Registry . . . . . . . . . . . . . . . . . . . . . . . . 56 8.14. CBOR Web Token Claims
8.13. JSON Web Token Claims . . . . . . . . . . . . . . . . . . 56 8.15. Media Type Registration
8.14. CBOR Web Token Claims . . . . . . . . . . . . . . . . . . 57 8.16. CoAP Content-Format Registry
8.15. Media Type Registrations . . . . . . . . . . . . . . . . 58 8.17. Expert Review Instructions
8.16. CoAP Content-Format Registry . . . . . . . . . . . . . . 58 9. References
8.17. Expert Review Instructions . . . . . . . . . . . . . . . 59 9.1. Normative References
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 60 9.2. Informative References
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 60 Appendix A. Design Justification
10.1. Normative References . . . . . . . . . . . . . . . . . . 60 Appendix B. Roles and Responsibilities
10.2. Informative References . . . . . . . . . . . . . . . . . 63 Appendix C. Requirements on Profiles
Appendix A. Design Justification . . . . . . . . . . . . . . . . 66 Appendix D. Assumptions on AS Knowledge about the C and RS
Appendix B. Roles and Responsibilities . . . . . . . . . . . . . 69 Appendix E. Differences to OAuth 2.0
Appendix C. Requirements on Profiles . . . . . . . . . . . . . . 71 Appendix F. Deployment Examples
Appendix D. Assumptions on AS Knowledge about C and RS . . . . . 72 F.1. Local Token Validation
Appendix E. Differences to OAuth 2.0 . . . . . . . . . . . . . . 73 F.2. Introspection Aided Token Validation
Appendix F. Deployment Examples . . . . . . . . . . . . . . . . 73 Acknowledgments
F.1. Local Token Validation . . . . . . . . . . . . . . . . . 74 Authors' Addresses
F.2. Introspection Aided Token Validation . . . . . . . . . . 78
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 82
1. Introduction 1. Introduction
Authorization is the process for granting approval to an entity to Authorization is the process for granting approval to an entity to
access a generic resource [RFC4949]. The authorization task itself access a generic resource [RFC4949]. The authorization task itself
can best be described as granting access to a requesting client, for can best be described as granting access to a requesting client for a
a resource hosted on a device, the resource server (RS). This resource hosted on a device, i.e., the resource server (RS). This
exchange is mediated by one or multiple authorization servers (AS). exchange is mediated by one or multiple authorization servers (ASes).
Managing authorization for a large number of devices and users can be Managing authorization for a large number of devices and users can be
a complex task. a complex task.
While prior work on authorization solutions for the Web and for the While prior work on authorization solutions for the Web and for the
mobile environment also applies to the Internet of Things (IoT) mobile environment also applies to the Internet of Things (IoT)
environment, many IoT devices are constrained, for example, in terms environment, many IoT devices are constrained, for example, in terms
of processing capabilities, available memory, etc. For such devices of processing capabilities, available memory, etc. For such devices,
the Constrained Application Protocol (CoAP) [RFC7252] can alleviate the Constrained Application Protocol (CoAP) [RFC7252] can alleviate
some resource concerns when used instead of HTTP to implement the some resource concerns when used instead of HTTP to implement the
communication flows of this specification. communication flows of this specification.
Appendix A gives an overview of the constraints considered in this Appendix A gives an overview of the constraints considered in this
design, and a more detailed treatment of constraints can be found in design, and a more detailed treatment of constraints can be found in
[RFC7228]. This design aims to accommodate different IoT deployments [RFC7228]. This design aims to accommodate different IoT deployments
and thus a continuous range of device and network capabilities. as well as a continuous range of device and network capabilities.
Taking energy consumption as an example: At one end there are energy- Taking energy consumption as an example, at one end, there are
harvesting or battery powered devices which have a tight power energy-harvesting or battery-powered devices that have a tight power
budget, on the other end there are mains-powered devices, and all budget; on the other end, there are mains-powered devices; and all
levels in between. levels exist in between.
Hence, IoT devices may be very different in terms of available Hence, IoT devices may be very different in terms of available
processing and message exchange capabilities and there is a need to processing and message exchange capabilities, and there is a need to
support many different authorization use cases [RFC7744]. support many different authorization use cases [RFC7744].
This specification describes a framework for authentication and This specification describes a framework for Authentication and
authorization in constrained environments (ACE) built on re-use of Authorization for Constrained Environments (ACE) built on reuse of
OAuth 2.0 [RFC6749], thereby extending authorization to Internet of OAuth 2.0 [RFC6749], thereby extending authorization to Internet of
Things devices. This specification contains the necessary building Things devices. This specification contains the necessary building
blocks for adjusting OAuth 2.0 to IoT environments. blocks for adjusting OAuth 2.0 to IoT environments.
Profiles of this framework are available in separate specifications, Profiles of this framework are available in separate specifications,
such as [I-D.ietf-ace-dtls-authorize] or such as [RFC9202] or [RFC9203]. Such profiles may specify the use of
[I-D.ietf-ace-oscore-profile]. Such profiles may specify the use of
the framework for a specific security protocol and the underlying the framework for a specific security protocol and the underlying
transports for use in a specific deployment environment to improve transports for use in a specific deployment environment to improve
interoperability. Implementations may claim conformance with a interoperability. Implementations may claim conformance with a
specific profile, whereby implementations utilizing the same profile specific profile, whereby implementations utilizing the same profile
interoperate, while implementations of different profiles are not interoperate, while implementations of different profiles are not
expected to be interoperable. More powerful devices, such as mobile expected to be interoperable. More powerful devices, such as mobile
phones and tablets, may implement multiple profiles and will phones and tablets, may implement multiple profiles and will
therefore be able to interact with a wider range of constrained therefore be able to interact with a wider range of constrained
devices. Requirements on profiles are described at contextually devices. Requirements on profiles are described at contextually
appropriate places throughout this specification, and also summarized appropriate places throughout this specification and also summarized
in Appendix C. in Appendix C.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
Certain security-related terms such as "authentication", Certain security-related terms, such as "authentication",
"authorization", "confidentiality", "(data) integrity", "message "authorization", "confidentiality", "(data) integrity", "message
authentication code", and "verify" are taken from [RFC4949]. authentication code", and "verify", are taken from [RFC4949].
Since exchanges in this specification are described as RESTful Since exchanges in this specification are described as RESTful
protocol interactions, HTTP [RFC7231] offers useful terminology. protocol interactions, HTTP [RFC7231] offers useful terminology.
(Note that "RESTful" refers to the Representational State Transfer
(REST) architecture.)
Terminology for entities in the architecture is defined in OAuth 2.0 Terminology for entities in the architecture is defined in OAuth 2.0
[RFC6749] such as client (C), resource server (RS), and authorization [RFC6749], such as client (C), resource server (RS), and
server (AS). authorization server (AS).
Note that the term "endpoint" is used here following its OAuth Note that the term "endpoint" is used here following its OAuth
definition, which is to denote resources such as token and definition, which is to denote resources, such as token and
introspection at the AS and authz-info at the RS (see Section 5.10.1 introspection at the AS and authz-info at the RS (see Section 5.10.1
for a definition of the authz-info endpoint). The CoAP [RFC7252] for a definition of the authz-info endpoint). The CoAP definition,
definition, which is "An entity participating in the CoAP protocol" which is "[a]n entity participating in the CoAP protocol" [RFC7252],
is not used in this specification. is not used in this specification.
The specifications in this document is called the "framework" or "ACE The specification in this document is called the "framework" or "ACE
framework". When referring to "profiles of this framework" it refers framework". When referring to "profiles of this framework", it
to additional specifications that define the use of this refers to additional specifications that define the use of this
specification with concrete transport and communication security specification with concrete transport and communication security
protocols (e.g., CoAP over DTLS). protocols (e.g., CoAP over DTLS).
The term "Access Information" is used for parameters, other than the The term "Access Information" is used for parameters, other than the
access token, provided to the client by the AS to enable it to access access token, provided to the client by the AS to enable it to access
the RS (e.g. public key of the RS, profile supported by RS). the RS (e.g., public key of the RS or profile supported by RS).
The term "Authorization Information" is used to denote all The term "authorization information" is used to denote all
information, including the claims of relevant access tokens, that an information, including the claims of relevant access tokens, that an
RS uses to determine whether an access request should be granted. RS uses to determine whether an access request should be granted.
3. Overview 3. Overview
This specification defines the ACE framework for authorization in the This specification defines the ACE framework for authorization in the
Internet of Things environment. It consists of a set of building Internet of Things environment. It consists of a set of building
blocks. blocks.
The basic block is the OAuth 2.0 [RFC6749] framework, which enjoys The basic block is the OAuth 2.0 [RFC6749] framework, which enjoys
widespread deployment. Many IoT devices can support OAuth 2.0 widespread deployment. Many IoT devices can support OAuth 2.0
without any additional extensions, but for certain constrained without any additional extensions, but for certain constrained
settings additional profiling is needed. settings, additional profiling is needed.
Another building block is the lightweight web transfer protocol CoAP Another building block is the lightweight web transfer protocol CoAP
[RFC7252], for those communication environments where HTTP is not [RFC7252], for those communication environments where HTTP is not
appropriate. CoAP typically runs on top of UDP, which further appropriate. CoAP typically runs on top of UDP, which further
reduces overhead and message exchanges. While this specification reduces overhead and message exchanges. While this specification
defines extensions for the use of OAuth over CoAP, other underlying defines extensions for the use of OAuth over CoAP, other underlying
protocols are not prohibited from being supported in the future, such protocols are not prohibited from being supported in the future, such
as HTTP/2 [RFC7540], Message Queuing Telemetry Transport (MQTT) as HTTP/2 [RFC7540], Message Queuing Telemetry Transport (MQTT)
[MQTT5.0], Bluetooth Low Energy (BLE) [BLE] and QUIC [MQTT5.0], Bluetooth Low Energy (BLE) [BLE], and QUIC [RFC9000].
[I-D.ietf-quic-transport]. Note that this document specifies Note that this document specifies protocol exchanges in terms of
protocol exchanges in terms of RESTful verbs such as GET and POST. RESTful verbs, such as GET and POST. Future profiles using protocols
Future profiles using protocols that do not support these verbs MUST that do not support these verbs MUST specify how the corresponding
specify how the corresponding protocol messages are transmitted protocol messages are transmitted instead.
instead.
A third building block is the Concise Binary Object Representation A third building block is the Concise Binary Object Representation
(CBOR) [RFC8949], for encodings where JSON [RFC8259] is not (CBOR) [RFC8949], for encodings where JSON [RFC8259] is not
sufficiently compact. CBOR is a binary encoding designed for small sufficiently compact. CBOR is a binary encoding designed for small
code and message size. Self-contained tokens and protocol message code and message size. Self-contained tokens and protocol message
payloads are encoded in CBOR when CoAP is used. When CoAP is not payloads are encoded in CBOR when CoAP is used. When CoAP is not
used, the use of CBOR remains RECOMMENDED. used, the use of CBOR remains RECOMMENDED.
A fourth building block is CBOR Object Signing and Encryption (COSE) A fourth building block is CBOR Object Signing and Encryption (COSE)
[RFC8152], which enables object-level layer security as an [RFC8152], which enables object-level layer security as an
alternative or complement to transport layer security (DTLS [RFC6347] alternative or complement to transport layer security (DTLS [RFC6347]
or TLS [RFC8446]). COSE is used to secure self-contained tokens such or TLS [RFC8446]). COSE is used to secure self-contained tokens,
as proof-of-possession (PoP) tokens, which are an extension to the such as proof-of-possession (PoP) tokens, which are an extension to
OAuth bearer tokens. The default token format is defined in CBOR Web the OAuth bearer tokens. The default token format is defined in CBOR
Token (CWT) [RFC8392]. Application-layer security for CoAP using Web Token (CWT) [RFC8392]. Application-layer security for CoAP using
COSE can be provided with OSCORE [RFC8613]. COSE can be provided with Object Security for Constrained RESTful
Environments (OSCORE) [RFC8613].
With the building blocks listed above, solutions satisfying various With the building blocks listed above, solutions satisfying various
IoT device and network constraints are possible. A list of IoT device and network constraints are possible. A list of
constraints is described in detail in [RFC7228] and a description of constraints is described in detail in [RFC7228], and a description of
how the building blocks mentioned above relate to the various how the building blocks mentioned above relate to the various
constraints can be found in Appendix A. constraints can be found in Appendix A.
Luckily, not every IoT device suffers from all constraints. The ACE Luckily, not every IoT device suffers from all constraints.
framework nevertheless takes all these aspects into account and Nevertheless, the ACE framework takes all these aspects into account
allows several different deployment variants to co-exist, rather than and allows several different deployment variants to coexist, rather
mandating a one-size-fits-all solution. It is important to cover the than mandating a one-size-fits-all solution. It is important to
wide range of possible interworking use cases and the different cover the wide range of possible interworking use cases and the
requirements from a security point of view. Once IoT deployments different requirements from a security point of view. Once IoT
mature, popular deployment variants will be documented in the form of deployments mature, popular deployment variants will be documented in
ACE profiles. the form of ACE profiles.
3.1. OAuth 2.0 3.1. OAuth 2.0
The OAuth 2.0 authorization framework enables a client to obtain The OAuth 2.0 authorization framework enables a client to obtain
scoped access to a resource with the permission of a resource owner. scoped access to a resource with the permission of a resource owner.
Authorization information, or references to it, is passed between the Authorization information, or references to it, is passed between the
nodes using access tokens. These access tokens are issued to clients nodes using access tokens. These access tokens are issued to clients
by an authorization server with the approval of the resource owner. by an authorization server with the approval of the resource owner.
The client uses the access token to access the protected resources The client uses the access token to access the protected resources
hosted by the resource server. hosted by the resource server.
A number of OAuth 2.0 terms are used within this specification: A number of OAuth 2.0 terms are used within this specification:
Access Tokens: Access Tokens:
Access tokens are credentials needed to access protected Access tokens are credentials needed to access protected
resources. An access token is a data structure representing resources. An access token is a data structure representing
authorization permissions issued by the AS to the client. Access authorization permissions issued by the AS to the client. Access
tokens are generated by the AS and consumed by the RS. The access tokens are generated by the AS and consumed by the RS. The access
token content is opaque to the client. token content is opaque to the client.
Access tokens can have different formats, and various methods of Access tokens can have different formats and various methods of
utilization e.g., cryptographic properties) based on the security utilization (e.g., cryptographic properties) based on the security
requirements of the given deployment. requirements of the given deployment.
Introspection: Introspection:
Introspection is a method for a resource server or potentially a Introspection is a method for a resource server, or potentially a
client, to query the authorization server for the active state and client, to query the authorization server for the active state and
content of a received access token. This is particularly useful content of a received access token. This is particularly useful
in those cases where the authorization decisions are very dynamic in those cases where the authorization decisions are very dynamic
and/or where the received access token itself is an opaque and/or where the received access token itself is an opaque
reference rather than a self-contained token. More information reference, rather than a self-contained token. More information
about introspection in OAuth 2.0 can be found in [RFC7662]. about introspection in OAuth 2.0 can be found in [RFC7662].
Refresh Tokens: Refresh Tokens:
Refresh tokens are credentials used to obtain access tokens. Refresh tokens are credentials used to obtain access tokens.
Refresh tokens are issued to the client by the authorization Refresh tokens are issued to the client by the authorization
server and are used to obtain a new access token when the current server and are used to obtain a new access token when the current
access token expires, or to obtain additional access tokens with access token expires or to obtain additional access tokens with
identical or narrower scope (such access tokens may have a shorter identical or narrower scope (such access tokens may have a shorter
lifetime and fewer permissions than authorized by the resource lifetime and fewer permissions than authorized by the resource
owner). Issuing a refresh token is optional at the discretion of owner). Issuing a refresh token is optional at the discretion of
the authorization server. If the authorization server issues a the authorization server. If the authorization server issues a
refresh token, it is included when issuing an access token (i.e., refresh token, it is included when issuing an access token (i.e.,
step (B) in Figure 1). step (B) in Figure 1).
A refresh token in OAuth 2.0 is a string representing the A refresh token in OAuth 2.0 is a string representing the
authorization granted to the client by the resource owner. The authorization granted to the client by the resource owner. The
string is usually opaque to the client. The token denotes an string is usually opaque to the client. The token denotes an
identifier used to retrieve the authorization information. Unlike identifier used to retrieve the authorization information. Unlike
access tokens, refresh tokens are intended for use only with access tokens, refresh tokens are intended for use only with
authorization servers and are never sent to resource servers. In authorization servers and are never sent to resource servers. In
this framework, refresh tokens are encoded in binary instead of this framework, refresh tokens are encoded in binary instead of
strings, if used. strings, if used.
Proof of Possession Tokens: Proof-of-Possession Tokens:
A token may be bound to a cryptographic key, which is then used to A token may be bound to a cryptographic key, which is then used to
bind the token to a request authorized by the token. Such tokens bind the token to a request authorized by the token. Such tokens
are called proof-of-possession tokens (or PoP tokens). are called proof-of-possession tokens (or PoP tokens).
The proof-of-possession security concept used here assumes that The proof-of-possession security concept used here assumes that
the AS acts as a trusted third party that binds keys to tokens. the AS acts as a trusted third party that binds keys to tokens.
In the case of access tokens, these so called PoP keys are then In the case of access tokens, these so-called PoP keys are then
used by the client to demonstrate the possession of the secret to used by the client to demonstrate the possession of the secret to
the RS when accessing the resource. The RS, when receiving an the RS when accessing the resource. The RS, when receiving an
access token, needs to verify that the key used by the client access token, needs to verify that the key used by the client
matches the one bound to the access token. When this matches the one bound to the access token. When this
specification uses the term "access token" it is assumed to be a specification uses the term "access token", it is assumed to be a
PoP access token unless specifically stated otherwise. PoP access token unless specifically stated otherwise.
The key bound to the token (the PoP key) may use either symmetric The key bound to the token (the PoP key) may use either symmetric
or asymmetric cryptography. The appropriate choice of the kind of or asymmetric cryptography. The appropriate choice of the kind of
cryptography depends on the constraints of the IoT devices as well cryptography depends on the constraints of the IoT devices as well
as on the security requirements of the use case. as on the security requirements of the use case.
Symmetric PoP key: Symmetric PoP key:
The AS generates a random symmetric PoP key. The key is either The AS generates a random, symmetric PoP key. The key is
stored to be returned on introspection calls or included in the either stored to be returned on introspection calls or included
token. Either the whole token or only the key MUST be in the token. Either the whole token or only the key MUST be
encrypted in the latter case. The PoP key is also returned to encrypted in the latter case. The PoP key is also returned to
client together with the token. client together with the token.
Asymmetric PoP key: Asymmetric PoP key:
An asymmetric key pair is generated by the client and the An asymmetric key pair is generated by the client and the
public key is sent to the AS (if it does not already have public key is sent to the AS (if it does not already have
knowledge of the client's public key). Information about the knowledge of the client's public key). Information about the
public key, which is the PoP key in this case, is either stored public key, which is the PoP key in this case, is either stored
to be returned on introspection calls or included inside the to be returned on introspection calls or included inside the
token and sent back to the client. The resource server token and sent back to the client. The resource server
consuming the token can identify the public key from the consuming the token can identify the public key from the
information in the token, which allows the client to use the information in the token, which allows the client to use the
corresponding private key for the proof of possession. corresponding private key for the proof of possession.
The token is either a simple reference, or a structured The token is either a simple reference or a structured information
information object (e.g., CWT [RFC8392]) protected by a object (e.g., CWT [RFC8392]) protected by a cryptographic wrapper
cryptographic wrapper (e.g., COSE [RFC8152]). The choice of PoP (e.g., COSE [RFC8152]). The choice of PoP key does not
key does not necessarily imply a specific credential type for the necessarily imply a specific credential type for the integrity
integrity protection of the token. protection of the token.
Scopes and Permissions: Scopes and Permissions:
In OAuth 2.0, the client specifies the type of permissions it is In OAuth 2.0, the client specifies the type of permissions it is
seeking to obtain (via the scope parameter) in the access token seeking to obtain (via the scope parameter) in the access token
request. In turn, the AS may use the scope response parameter to request. In turn, the AS may use the scope response parameter to
inform the client of the scope of the access token issued. As the inform the client of the scope of the access token issued. As the
client could be a constrained device as well, this specification client could be a constrained device as well, this specification
defines the use of CBOR encoding, see Section 5, for such requests defines the use of CBOR encoding (see Section 5) for such requests
and responses. and responses.
The values of the scope parameter in OAuth 2.0 are expressed as a The values of the scope parameter in OAuth 2.0 are expressed as a
list of space-delimited, case-sensitive strings, with a semantic list of space-delimited, case-sensitive strings with a semantic
that is well-known to the AS and the RS. More details about the that is well known to the AS and the RS. More details about the
concept of scopes is found under Section 3.3 in [RFC6749]. concept of scopes are found under Section 3.3 of [RFC6749].
Claims: Claims:
Information carried in the access token or returned from Information carried in the access token or returned from
introspection, called claims, is in the form of name-value pairs. introspection, called claims, is in the form of name-value pairs.
An access token may, for example, include a claim identifying the An access token may, for example, include a claim identifying the
AS that issued the token (via the "iss" claim) and what audience AS that issued the token (via the "iss" claim) and what audience
the access token is intended for (via the "aud" claim). The the access token is intended for (via the "aud" claim). The
audience of an access token can be a specific resource or one or audience of an access token can be a specific resource, one
many resource servers. The resource owner policies influence what resource, or many resource servers. The resource owner policies
claims are put into the access token by the authorization server. influence what claims are put into the access token by the
authorization server.
While the structure and encoding of the access token varies While the structure and encoding of the access token varies
throughout deployments, a standardized format has been defined throughout deployments, a standardized format has been defined
with the JSON Web Token (JWT) [RFC7519] where claims are encoded with the JSON Web Token (JWT) [RFC7519], where claims are encoded
as a JSON object. In [RFC8392] the CBOR Web Token (CWT) has been as a JSON object. In [RFC8392], the CBOR Web Token (CWT) has been
defined as an equivalent format using CBOR encoding. defined as an equivalent format using CBOR encoding.
The token and introspection Endpoints: Token and Introspection Endpoints:
The AS hosts the token endpoint that allows a client to request The AS hosts the token endpoint that allows a client to request
access tokens. The client makes a POST request to the token access tokens. The client makes a POST request to the token
endpoint on the AS and receives the access token in the response endpoint on the AS and receives the access token in the response
(if the request was successful). (if the request was successful).
In some deployments, a token introspection endpoint is provided by In some deployments, a token introspection endpoint is provided by
the AS, which can be used by the RS and potentially the client, if the AS, which can be used by the RS and potentially the client, if
they need to request additional information regarding a received they need to request additional information regarding a received
access token. The requesting entity makes a POST request to the access token. The requesting entity makes a POST request to the
introspection endpoint on the AS and receives information about introspection endpoint on the AS and receives information about
the access token in the response. (See "Introspection" above.) the access token in the response. (See "Introspection" above.)
3.2. CoAP 3.2. CoAP
CoAP is an application-layer protocol similar to HTTP, but CoAP is an application-layer protocol similar to HTTP but
specifically designed for constrained environments. CoAP typically specifically designed for constrained environments. CoAP typically
uses datagram-oriented transport, such as UDP, where reordering and uses datagram-oriented transport, such as UDP, where reordering and
loss of packets can occur. A security solution needs to take the loss of packets can occur. A security solution needs to take the
latter aspects into account. latter aspects into account.
While HTTP uses headers and query strings to convey additional While HTTP uses headers and query strings to convey additional
information about a request, CoAP encodes such information into information about a request, CoAP encodes such information into
header parameters called 'options'. header parameters called 'options'.
CoAP supports application-layer fragmentation of the CoAP payloads CoAP supports application-layer fragmentation of the CoAP payloads
through blockwise transfers [RFC7959]. However, blockwise transfer through block-wise transfers [RFC7959]. However, block-wise transfer
does not increase the size limits of CoAP options, therefore data does not increase the size limits of CoAP options; therefore, data
encoded in options has to be kept small. encoded in options has to be kept small.
Transport layer security for CoAP can be provided by DTLS or TLS Transport layer security for CoAP can be provided by DTLS or TLS
[RFC6347][RFC8446] [I-D.ietf-tls-dtls13]. CoAP defines a number of [RFC6347] [RFC8446] [RFC9147]. CoAP defines a number of proxy
proxy operations that require transport layer security to be operations that require transport layer security to be terminated at
terminated at the proxy. One approach for protecting CoAP the proxy. One approach for protecting CoAP communication end-to-end
communication end-to-end through proxies, and also to support through proxies, and also to support security for CoAP over a
security for CoAP over a different transport in a uniform way, is to different transport in a uniform way, is to provide security at the
provide security at the application layer using an object-based application layer using an object-based security mechanism, such as
security mechanism such as COSE [RFC8152]. COSE [RFC8152].
One application of COSE is OSCORE [RFC8613], which provides end-to- One application of COSE is OSCORE [RFC8613], which provides end-to-
end confidentiality, integrity and replay protection, and a secure end confidentiality, integrity and replay protection, and a secure
binding between CoAP request and response messages. In OSCORE, the binding between CoAP request and response messages. In OSCORE, the
CoAP messages are wrapped in COSE objects and sent using CoAP. CoAP messages are wrapped in COSE objects and sent using CoAP.
In this framework the use of CoAP as replacement for HTTP is In this framework, the use of CoAP as replacement for HTTP is
RECOMMENDED for use in constrained environments. For communication RECOMMENDED for use in constrained environments. For communication
security this framework does not make an explicit protocol security, this framework does not make an explicit protocol
recommendation, since the choice depends on the requirements of the recommendation, since the choice depends on the requirements of the
specific application. DTLS [RFC6347], [I-D.ietf-tls-dtls13] and specific application. DTLS [RFC6347] [RFC9147] and OSCORE [RFC8613]
OSCORE [RFC8613] are mentioned as examples, other protocols are mentioned as examples; other protocols fulfilling the
fulfilling the requirements from Section 6.5 are also applicable. requirements from Section 6.5 are also applicable.
4. Protocol Interactions 4. Protocol Interactions
The ACE framework is based on the OAuth 2.0 protocol interactions The ACE framework is based on the OAuth 2.0 protocol interactions
using the token endpoint and optionally the introspection endpoint. using the token endpoint and optionally the introspection endpoint.
A client obtains an access token, and optionally a refresh token, A client obtains an access token, and optionally a refresh token,
from an AS using the token endpoint and subsequently presents the from an AS using the token endpoint and subsequently presents the
access token to an RS to gain access to a protected resource. In access token to an RS to gain access to a protected resource. In
most deployments the RS can process the access token locally, however most deployments, the RS can process the access token locally;
in some cases the RS may present it to the AS via the introspection however, in some cases, the RS may present it to the AS via the
endpoint to get fresh information. These interactions are shown in introspection endpoint to get fresh information. These interactions
Figure 1. An overview of various OAuth concepts is provided in are shown in Figure 1. An overview of various OAuth concepts is
Section 3.1. provided in Section 3.1.
+--------+ +---------------+ +--------+ +---------------+
| |---(A)-- Token Request ------->| | | |---(A)-- Token Request ------->| |
| | | Authorization | | | | Authorization |
| |<--(B)-- Access Token ---------| Server | | |<--(B)-- Access Token ---------| Server |
| | + Access Information | | | | + Access Information | |
| | + Refresh Token (optional) +---------------+ | | + Refresh Token (optional) +---------------+
| | ^ | | | ^ |
| | Introspection Request (D)| | | | Introspection Request (D)| |
| Client | Response | |(E) | Client | Response | |(E)
| | (optional exchange) | | | | (optional exchange) | |
| | | v | | | v
| | +--------------+ | | +--------------+
| |---(C)-- Token + Request ----->| | | |---(C)-- Token + Request ----->| |
| | | Resource | | | | Resource |
| |<--(F)-- Protected Resource ---| Server | | |<--(F)-- Protected Resource ---| Server |
| | | | | | | |
+--------+ +--------------+ +--------+ +--------------+
Figure 1: Basic Protocol Flow. Figure 1: Basic Protocol Flow
Requesting an Access Token (A): Requesting an Access Token (A):
The client makes an access token request to the token endpoint at The client makes an access token request to the token endpoint at
the AS. This framework assumes the use of PoP access tokens (see the AS. This framework assumes the use of PoP access tokens (see
Section 3.1 for a short description) wherein the AS binds a key to Section 3.1 for a short description) wherein the AS binds a key to
an access token. The client may include permissions it seeks to an access token. The client may include permissions it seeks to
obtain, and information about the credentials it wants to use for obtain and information about the credentials it wants to use for
proof-of-possession (e.g., symmetric/asymmetric cryptography or a proof of possession (e.g., symmetric/asymmetric cryptography or a
reference to a specific key) of the access token. reference to a specific key) of the access token.
Access Token Response (B): Access Token Response (B):
If the request from the client has been successfully verified, If the request from the client has been successfully verified,
authenticated, and authorized, the AS returns an access token and authenticated, and authorized, the AS returns an access token and
optionally a refresh token. Note that only certain grant types optionally a refresh token. Note that only certain grant types
support refresh tokens. The AS can also return additional support refresh tokens. The AS can also return additional
parameters, referred to as "Access Information". In addition to parameters, referred to as "Access Information". In addition to
the response parameters defined by OAuth 2.0 and the PoP access the response parameters defined by OAuth 2.0 and the PoP access
token extension, this framework defines parameters that can be token extension, this framework defines parameters that can be
used to inform the client about capabilities of the RS, e.g. the used to inform the client about capabilities of the RS, e.g., the
profile the RS supports. More information about these parameters profile the RS supports. More information about these parameters
can be found in Section 5.8.4. can be found in Section 5.8.4.
Resource Request (C): Resource Request (C):
The client interacts with the RS to request access to the The client interacts with the RS to request access to the
protected resource and provides the access token. The protocol to protected resource and provides the access token. The protocol to
use between the client and the RS is not restricted to CoAP. use between the client and the RS is not restricted to CoAP.
HTTP, HTTP/2 [RFC7540], QUIC [I-D.ietf-quic-transport], MQTT HTTP, HTTP/2 [RFC7540], QUIC [RFC9000], MQTT [MQTT5.0], Bluetooth
[MQTT5.0], Bluetooth Low Energy [BLE], etc., are also viable Low Energy [BLE], etc., are also viable candidates.
candidates.
Depending on the device limitations and the selected protocol, Depending on the device limitations and the selected protocol,
this exchange may be split up into two parts: this exchange may be split up into two parts:
(1) the client sends the access token containing, or (1) the client sends the access token containing, or referencing,
referencing, the authorization information to the RS, that will the authorization information to the RS that will be used for
be used for subsequent resource requests by the client, and subsequent resource requests by the client, and
(2) the client makes the resource access request, using the (2) the client makes the resource access request using the
communication security protocol and other Access Information communication security protocol and other Access Information
obtained from the AS. obtained from the AS.
The client and the RS mutually authenticate using the security The client and the RS mutually authenticate using the security
protocol specified in the profile (see step B) and the keys protocol specified in the profile (see step (B)) and the keys
obtained in the access token or the Access Information. The RS obtained in the access token or the Access Information. The RS
verifies that the token is integrity protected and originated by verifies that the token is integrity protected and originated by
the AS. It then compares the claims contained in the access token the AS. It then compares the claims contained in the access token
with the resource request. If the RS is online, validation can be with the resource request. If the RS is online, validation can be
handed over to the AS using token introspection (see messages D handed over to the AS using token introspection (see messages (D)
and E) over HTTP or CoAP. and (E)) over HTTP or CoAP.
Token Introspection Request (D): Token Introspection Request (D):
A resource server may be configured to introspect the access token A resource server may be configured to introspect the access token
by including it in a request to the introspection endpoint at that by including it in a request to the introspection endpoint at that
AS. Token introspection over CoAP is defined in Section 5.9 and AS. Token introspection over CoAP is defined in Section 5.9 and
for HTTP in [RFC7662]. for HTTP in [RFC7662].
Note that token introspection is an optional step and can be Note that token introspection is an optional step and can be
omitted if the token is self-contained and the resource server is omitted if the token is self-contained and the resource server is
prepared to perform the token validation on its own. prepared to perform the token validation on its own.
Token Introspection Response (E): Token Introspection Response (E):
The AS validates the token and returns the most recent parameters, The AS validates the token and returns the most recent parameters,
such as scope, audience, validity etc. associated with it back to such as scope, audience, validity, etc., associated with it back
the RS. The RS then uses the received parameters to process the to the RS. The RS then uses the received parameters to process
request to either accept or to deny it. the request to either accept or to deny it.
Protected Resource (F): Protected Resource (F):
If the request from the client is authorized, the RS fulfills the If the request from the client is authorized, the RS fulfills the
request and returns a response with the appropriate response code. request and returns a response with the appropriate response code.
The RS uses the dynamically established keys to protect the The RS uses the dynamically established keys to protect the
response, according to the communication security protocol used. response according to the communication security protocol used.
The OAuth 2.0 framework defines a number of "protocol flows" via The OAuth 2.0 framework defines a number of "protocol flows" via
grant types, which have been extended further with extensions to grant types, which have been extended further with extensions to
OAuth 2.0 (such as [RFC7521] and [RFC8628]). What grant type works OAuth 2.0 (such as [RFC7521] and [RFC8628]). What grant type works
best depends on the usage scenario and [RFC7744] describes many best depends on the usage scenario; [RFC7744] describes many
different IoT use cases but there are two grant types that cover a different IoT use cases, but there are two grant types that cover a
majority of these scenarios, namely the Authorization Code Grant majority of these scenarios, namely the authorization code grant
(described in Section 4.1 of [RFC7521]) and the Client Credentials (described in Section 4.1 of [RFC7521]) and the client credentials
Grant (described in Section 4.4 of [RFC7521]). The Authorization grant (described in Section 4.4 of [RFC6749]). The authorization
Code Grant is a good fit for use with apps running on smart phones code grant is a good fit for use with apps running on smartphones and
and tablets that request access to IoT devices, a common scenario in tablets that request access to IoT devices, a common scenario in the
the smart home environment, where users need to go through an smart home environment, where users need to go through an
authentication and authorization phase (at least during the initial authentication and authorization phase (at least during the initial
setup phase). The native apps guidelines described in [RFC8252] are setup phase). The native apps guidelines described in [RFC8252] are
applicable to this use case. The Client Credential Grant is a good applicable to this use case. The client credentials grant is a good
fit for use with IoT devices where the OAuth client itself is fit for use with IoT devices where the OAuth client itself is
constrained. In such a case, the resource owner has pre-arranged constrained. In such a case, the resource owner has prearranged
access rights for the client with the authorization server, which is access rights for the client with the authorization server, which is
often accomplished using a commissioning tool. often accomplished using a commissioning tool.
The consent of the resource owner, for giving a client access to a The consent of the resource owner, for giving a client access to a
protected resource, can be provided dynamically as in the traditional protected resource, can be provided dynamically as in the traditional
OAuth flows, or it could be pre-configured by the resource owner as OAuth flows, or it could be preconfigured by the resource owner as
authorization policies at the AS, which the AS evaluates when a token authorization policies at the AS, which the AS evaluates when a token
request arrives. The resource owner and the requesting party (i.e., request arrives. The resource owner and the requesting party (i.e.,
client owner) are not shown in Figure 1. client owner) are not shown in Figure 1.
This framework supports a wide variety of communication security This framework supports a wide variety of communication security
mechanisms between the ACE entities, such as client, AS, and RS. It mechanisms between the ACE entities, such as the client, AS, and RS.
is assumed that the client has been registered (also called enrolled It is assumed that the client has been registered (also called
or onboarded) to an AS using a mechanism defined outside the scope of enrolled or onboarded) to an AS using a mechanism defined outside the
this document. In practice, various techniques for onboarding have scope of this document. In practice, various techniques for
been used, such as factory-based provisioning or the use of onboarding have been used, such as factory-based provisioning or the
commissioning tools. Regardless of the onboarding technique, this use of commissioning tools. Regardless of the onboarding technique,
provisioning procedure implies that the client and the AS exchange this provisioning procedure implies that the client and the AS
credentials and configuration parameters. These credentials are used exchange credentials and configuration parameters. These credentials
to mutually authenticate each other and to protect messages exchanged are used to mutually authenticate each other and to protect messages
between the client and the AS. exchanged between the client and the AS.
It is also assumed that the RS has been registered with the AS, It is also assumed that the RS has been registered with the AS,
potentially in a similar way as the client has been registered with potentially in a similar way as the client has been registered with
the AS. Established keying material between the AS and the RS allows the AS. Established keying material between the AS and the RS allows
the AS to apply cryptographic protection to the access token to the AS to apply cryptographic protection to the access token to
ensure that its content cannot be modified, and if needed, that the ensure that its content cannot be modified and, if needed, that the
content is confidentiality protected. Confidentiality protection of content is confidentiality protected. Confidentiality protection of
the access token content would be provided on top of confidentiality the access token content would be provided on top of confidentiality
protection via a communication security protocol. protection via a communication security protocol.
The keying material necessary for establishing communication security The keying material necessary for establishing communication security
between C and RS is dynamically established as part of the protocol between the C and RS is dynamically established as part of the
described in this document. protocol described in this document.
At the start of the protocol, there is an optional discovery step At the start of the protocol, there is an optional discovery step
where the client discovers the resource server and the resources this where the client discovers the resource server and the resources this
server hosts. In this step, the client might also determine what server hosts. In this step, the client might also determine what
permissions are needed to access the protected resource. A generic permissions are needed to access the protected resource. A generic
procedure is described in Section 5.1; profiles MAY define other procedure is described in Section 5.1; profiles MAY define other
procedures for discovery. procedures for discovery.
In Bluetooth Low Energy, for example, advertisements are broadcast by In Bluetooth Low Energy, for example, advertisements are broadcast by
a peripheral, including information about the primary services. In a peripheral, including information about the primary services. In
CoAP, as a second example, a client can make a request to "/.well- CoAP, as a second example, a client can make a request to "/.well-
known/core" to obtain information about available resources, which known/core" to obtain information about available resources, which
are returned in a standardized format as described in [RFC6690]. are returned in a standardized format, as described in [RFC6690].
5. Framework 5. Framework
The following sections detail the profiling and extensions of OAuth The following sections detail the profiling and extensions of OAuth
2.0 for constrained environments, which constitutes the ACE 2.0 for constrained environments, which constitutes the ACE
framework. framework.
Credential Provisioning Credential Provisioning
In constrained environments it cannot be assumed that the client In constrained environments, it cannot be assumed that the client
and the RS are part of a common key infrastructure. Therefore, and the RS are part of a common key infrastructure. Therefore,
the AS provisions credentials and associated information to allow the AS provisions credentials and associated information to allow
mutual authentication between the client and the RS. The mutual authentication between the client and the RS. The
resulting security association between the client and the RS may resulting security association between the client and the RS may
then also be used to bind these credentials to the access tokens then also be used to bind these credentials to the access tokens
the client uses. the client uses.
Proof-of-Possession Proof of Possession
The ACE framework, by default, implements proof-of-possession for The ACE framework, by default, implements proof of possession for
access tokens, i.e., that the token holder can prove being a access tokens, i.e., that the token holder can prove being a
holder of the key bound to the token. The binding is provided by holder of the key bound to the token. The binding is provided by
the "cnf" claim [RFC8747] indicating what key is used for proof- the "cnf" (confirmation) claim [RFC8747], indicating what key is
of-possession. If a client needs to submit a new access token, used for proof of possession. If a client needs to submit a new
e.g., to obtain additional access rights, they can request that access token, e.g., to obtain additional access rights, they can
the AS binds this token to the same key as the previous one. request that the AS binds this token to the same key as the
previous one.
ACE Profiles ACE Profiles
The client or RS may be limited in the encodings or protocols it The client or RS may be limited in the encodings or protocols it
supports. To support a variety of different deployment settings, supports. To support a variety of different deployment settings,
specific interactions between client and RS are defined in an ACE specific interactions between the client and RS are defined in an
profile. In ACE framework the AS is expected to manage the ACE profile. In the ACE framework, the AS is expected to manage
matching of compatible profile choices between a client and an RS. the matching of compatible profile choices between a client and an
The AS informs the client of the selected profile using the RS. The AS informs the client of the selected profile using the
"ace_profile" parameter in the token response. "ace_profile" parameter in the token response.
OAuth 2.0 requires the use of TLS both to protect the communication OAuth 2.0 requires the use of TLS to protect the communication
between AS and client when requesting an access token; between client between the AS and client when requesting an access token between the
and RS when accessing a resource and between AS and RS if client and RS when accessing a resource and between the AS and RS if
introspection is used. In constrained settings TLS is not always introspection is used. In constrained settings, TLS is not always
feasible, or desirable. Nevertheless it is REQUIRED that the feasible or desirable. Nevertheless, it is REQUIRED that the
communications named above are encrypted, integrity protected and communications named above are encrypted, integrity protected, and
protected against message replay. It is also REQUIRED that the protected against message replay. It is also REQUIRED that the
communicating endpoints perform mutual authentication. Furthermore communicating endpoints perform mutual authentication. Furthermore,
it MUST be assured that responses are bound to the requests in the it MUST be assured that responses are bound to the requests in the
sense that the receiver of a response can be certain that the sense that the receiver of a response can be certain that the
response actually belongs to a certain request. Note that setting up response actually belongs to a certain request. Note that setting up
such a secure communication may require some unprotected messages to such a secure communication may require some unprotected messages to
be exchanged first (e.g. sending the token from the client to the be exchanged first (e.g., sending the token from the client to the
RS). RS).
Profiles MUST specify a communication security protocol between Profiles MUST specify a communication security protocol between the
client and RS that provides the features required above. Profiles client and RS that provides the features required above. Profiles
MUST specify a communication security protocol RECOMMENDED to be used MUST specify a communication security protocol RECOMMENDED to be used
between client and AS that provides the features required above. between the client and AS that provides the features required above.
Profiles MUST specify for introspection a communication security Profiles MUST specify, for introspection, a communication security
protocol RECOMMENDED to be used between RS and AS that provides the protocol RECOMMENDED to be used between the RS and AS that provides
features required above. These recommendations enable the features required above. These recommendations enable
interoperability between different implementations without the need interoperability between different implementations without the need
to define a new profile if the communication between C and AS, or to define a new profile if the communication between the C and AS, or
between RS and AS, is protected with a different security protocol between the RS and AS, is protected with a different security
complying with the security requirements above. protocol complying with the security requirements above.
In OAuth 2.0 the communication with the Token and the Introspection In OAuth 2.0, the communication with the Token and the Introspection
endpoints at the AS is assumed to be via HTTP and may use Uri-query endpoints at the AS is assumed to be via HTTP and may use Uri-query
parameters. When profiles of this framework use CoAP instead, it is parameters. When profiles of this framework use CoAP instead, it is
REQUIRED to use of the following alternative instead of Uri-query REQUIRED to use of the following alternative instead of Uri-query
parameters: The sender (client or RS) encodes the parameters of its parameters: The sender (client or RS) encodes the parameters of its
request as a CBOR map and submits that map as the payload of the POST request as a CBOR map and submits that map as the payload of the POST
request. The CBOR encoding for a number of OAuth 2.0 parameters is request. The CBOR encoding for a number of OAuth 2.0 parameters is
specified in this document, if a profile needs to use other OAuth 2.0 specified in this document; if a profile needs to use other OAuth 2.0
parameters with CoAP it MUST specify their CBOR encoding. parameters with CoAP, it MUST specify their CBOR encoding.
Profiles that use CBOR encoding of protocol message parameters at the Profiles that use CBOR encoding of protocol message parameters at the
outermost encoding layer MUST use the content format 'application/ outermost encoding layer MUST use the Content-Format "application/
ace+cbor'. If CoAP is used for communication, the Content-Format ace+cbor". If CoAP is used for communication, the Content-Format
MUST be abbreviated with the ID: 19 (see Section 8.16). MUST be abbreviated with the ID: 19 (see Section 8.16).
The OAuth 2.0 AS uses a JSON structure in the payload of its The OAuth 2.0 AS uses a JSON structure in the payload of its
responses both to client and RS. If CoAP is used, it is REQUIRED to responses both to the client and RS. If CoAP is used, it is REQUIRED
use CBOR [RFC8949] instead of JSON. Depending on the profile, the to use CBOR [RFC8949] instead of JSON. Depending on the profile, the
CBOR payload MAY be enclosed in a non-CBOR cryptographic wrapper. CBOR payload MAY be enclosed in a non-CBOR cryptographic wrapper.
5.1. Discovering Authorization Servers 5.1. Discovering Authorization Servers
C must discover the AS in charge of RS to determine where to request The C must discover the AS in charge of the RS to determine where to
the access token. To do so, C must 1. find out the AS URI to which request the access token. To do so, the C 1) must find out the AS
the token request message must be sent and 2. MUST validate that the URI to which the token request message must be sent and 2) MUST
AS with this URI is authorized to provide access tokens for this RS. validate that the AS with this URI is authorized to provide access
tokens for this RS.
In order to determine the AS URI, C MAY send an initial Unauthorized In order to determine the AS URI, the C MAY send an initial
Resource Request message to RS. RS then denies the request and sends Unauthorized Resource Request message to the RS. The RS then denies
the address of its AS back to C (see Section 5.2). How C validates the request and sends the address of its AS back to the C (see
the AS authorization is not in scope for this document. C may, e.g., Section 5.2). How the C validates the AS authorization is not in
ask its owner if this AS is authorized for this RS. C may also use a scope for this document. The C may, for example, ask its owner if
mechanism that addresses both problems at once (e.g. by querying a this AS is authorized for this RS. The C may also use a mechanism
dedicated secure service provided by the client owner) . that addresses both problems at once (e.g., by querying a dedicated
secure service provided by the client owner) .
5.2. Unauthorized Resource Request Message 5.2. Unauthorized Resource Request Message
An Unauthorized Resource Request message is a request for any An Unauthorized Resource Request message is a request for any
resource hosted by RS for which the client does not have resource hosted by the RS for which the client does not have
authorization granted. RSes MUST treat any request for a protected authorization granted. The RSs MUST treat any request for a
resource as an Unauthorized Resource Request message when any of the protected resource as an Unauthorized Resource Request message when
following hold: any of the following hold:
* The request has been received on an unsecured channel. * The request has been received on an unsecured channel.
* The RS has no valid access token for the sender of the request * The RS has no valid access token for the sender of the request
regarding the requested action on that resource. regarding the requested action on that resource.
* The RS has a valid access token for the sender of the request, but * The RS has a valid access token for the sender of the request, but
that token does not authorize the requested action on the that token does not authorize the requested action on the
requested resource. requested resource.
Note: These conditions ensure that the RS can handle requests Note: These conditions ensure that the RS can handle requests
autonomously once access was granted and a secure channel has been autonomously once access was granted and a secure channel has been
established between C and RS. The authz-info endpoint, as part of established between the C and RS. The authz-info endpoint, as part
the process for authorizing to protected resources, is not itself a of the process for authorizing to protected resources, is not itself
protected resource and MUST NOT be protected as specified above (cf. a protected resource and MUST NOT be protected as specified above
Section 5.10.1). (cf. Section 5.10.1).
Unauthorized Resource Request messages MUST be denied with an Unauthorized Resource Request messages MUST be denied with an
"unauthorized_client" error response. In this response, the Resource "unauthorized_client" error response. In this response, the resource
Server SHOULD provide proper "AS Request Creation Hints" to enable server SHOULD provide proper "AS Request Creation Hints" to enable
the client to request an access token from RS's AS as described in the client to request an access token from the RS's AS, as described
Section 5.3. in Section 5.3.
The handling of all client requests (including unauthorized ones) by The handling of all client requests (including unauthorized ones) by
the RS is described in Section 5.10.2. the RS is described in Section 5.10.2.
5.3. AS Request Creation Hints 5.3. AS Request Creation Hints
The "AS Request Creation Hints" message is sent by an RS as a The "AS Request Creation Hints" message is sent by an RS as a
response to an Unauthorized Resource Request message (see response to an Unauthorized Resource Request message (see
Section 5.2) to help the sender of the Unauthorized Resource Request Section 5.2) to help the sender of the Unauthorized Resource Request
message acquire a valid access token. The "AS Request Creation message acquire a valid access token. The "AS Request Creation
Hints" message is a CBOR or JSON map, with an OPTIONAL element "AS" Hints" message is a CBOR or JSON map, with an OPTIONAL element "AS"
specifying an absolute URI (see Section 4.3 of [RFC3986]) that specifying an absolute URI (see Section 4.3 of [RFC3986]) that
identifies the appropriate AS for the RS. identifies the appropriate AS for the RS.
The message can also contain the following OPTIONAL parameters: The message can also contain the following OPTIONAL parameters:
* A "audience" element contains an identifier the client should * An "audience" element contains an identifier the client should
request at the AS, as suggested by the RS. With this parameter, request at the AS, as suggested by the RS. With this parameter,
when included in the access token request to the AS, the AS is when included in the access token request to the AS, the AS is
able to restrict the use of access token to specific RSs. See able to restrict the use of the access token to specific RSs. See
Section 6.9 for a discussion of this parameter. Section 6.9 for a discussion of this parameter.
* A "kid" element containing the key identifier of a key used in an * A "kid" (key identifier) element contains the key identifier of a
existing security association between the client and the RS. The key used in an existing security association between the client
RS expects the client to request an access token bound to this and the RS. The RS expects the client to request an access token
key, in order to avoid having to re-establish the security bound to this key in order to avoid having to reestablish the
association. security association.
* A "cnonce" element containing a client-nonce. See Section 5.3.1. * A "cnonce" element contains a client-nonce. See Section 5.3.1.
* A "scope" element containing the suggested scope that the client * A "scope" element contains the suggested scope that the client
should request towards the AS. should request towards the AS.
Figure 2 summarizes the parameters that may be part of the "AS Table 1 summarizes the parameters that may be part of the "AS Request
Request Creation Hints". Creation Hints".
/-----------+----------+---------------------\ +==========+==========+=====================+
| Name | CBOR Key | Value Type | | Name | CBOR Key | Value Type |
|-----------+----------+---------------------| +==========+==========+=====================+
| AS | 1 | text string | | AS | 1 | text string |
| kid | 2 | byte string | +----------+----------+---------------------+
| audience | 5 | text string | | kid | 2 | byte string |
| scope | 9 | text or byte string | +----------+----------+---------------------+
| cnonce | 39 | byte string | | audience | 5 | text string |
\-----------+----------+---------------------/ +----------+----------+---------------------+
| scope | 9 | text or byte string |
+----------+----------+---------------------+
| cnonce | 39 | byte string |
+----------+----------+---------------------+
Figure 2: AS Request Creation Hints Table 1: AS Request Creation Hints
Note that the schema part of the AS parameter may need to be adapted Note that the schema part of the AS parameter may need to be adapted
to the security protocol that is used between the client and the AS. to the security protocol that is used between the client and the AS.
Thus the example AS value "coap://as.example.com/token" might need to Thus, the example AS value "coap://as.example.com/token" might need
be transformed to "coaps://as.example.com/token". It is assumed that to be transformed to "coaps://as.example.com/token". It is assumed
the client can determine the correct schema part on its own depending that the client can determine the correct schema part on its own
on the way it communicates with the AS. depending on the way it communicates with the AS.
Figure 3 shows an example for an "AS Request Creation Hints" message Figure 2 shows an example for an "AS Request Creation Hints" message
payload using CBOR [RFC8949] diagnostic notation, using the parameter payload using CBOR [RFC8949] diagnostic notation, using the parameter
names instead of the CBOR keys for better human readability. names instead of the CBOR keys for better human readability.
4.01 Unauthorized 4.01 Unauthorized
Content-Format: application/ace+cbor Content-Format: application/ace+cbor
Payload : Payload :
{ {
"AS" : "coaps://as.example.com/token", "AS" : "coaps://as.example.com/token",
"audience" : "coaps://rs.example.com" "audience" : "coaps://rs.example.com"
"scope" : "rTempC", "scope" : "rTempC",
"cnonce" : h'e0a156bb3f' "cnonce" : h'e0a156bb3f'
} }
Figure 3: AS Request Creation Hints payload example Figure 2: AS Request Creation Hints Payload Example
In the example above, the response parameter "AS" points the receiver In the example above, the response parameter "AS" points the receiver
of this message to the URI "coaps://as.example.com/token" to request of this message to the URI "coaps://as.example.com/token" to request
access tokens. The RS sending this response uses an internal clock access tokens. The RS sending this response uses an internal clock
that is not synchronized with the clock of the AS. Therefore, it can that is not synchronized with the clock of the AS. Therefore, it
not reliably verify the expiration time of access tokens it receives. cannot reliably verify the expiration time of access tokens it
To ensure a certain level of access token freshness nevertheless, the receives. Nevertheless, to ensure a certain level of access token
RS has included a "cnonce" parameter (see Section 5.3.1) in the freshness, the RS has included a cnonce parameter (see Section 5.3.1)
response. (The hex-sequence of the cnonce parameter is encoded in in the response. (The hex sequence of the cnonce parameter is
CBOR-based notation in this example.) encoded in CBOR-based notation in this example.)
Figure 4 illustrates the mandatory to use binary encoding of the
message payload shown in Figure 3. Figure 3 illustrates the mandatory use of binary encoding of the
message payload shown in Figure 2.
a4 # map(4) a4 # map(4)
01 # unsigned(1) (=AS) 01 # unsigned(1) (=AS)
78 1c # text(28) 78 1c # text(28)
636f6170733a2f2f61732e657861 636f6170733a2f2f61732e657861
6d706c652e636f6d2f746f6b656e # "coaps://as.example.com/token" 6d706c652e636f6d2f746f6b656e # "coaps://as.example.com/token"
05 # unsigned(5) (=audience) 05 # unsigned(5) (=audience)
76 # text(22) 76 # text(22)
636f6170733a2f2f72732e657861 636f6170733a2f2f72732e657861
6d706c652e636f6d # "coaps://rs.example.com" 6d706c652e636f6d # "coaps://rs.example.com"
09 # unsigned(9) (=scope) 09 # unsigned(9) (=scope)
66 # text(6) 66 # text(6)
7254656d7043 # "rTempC" 7254656d7043 # "rTempC"
18 27 # unsigned(39) (=cnonce) 18 27 # unsigned(39) (=cnonce)
45 # bytes(5) 45 # bytes(5)
e0a156bb3f # e0a156bb3f #
Figure 4: AS Request Creation Hints example encoded in CBOR Figure 3: AS Request Creation Hints Example Encoded in CBOR
5.3.1. The Client-Nonce Parameter 5.3.1. The Client-Nonce Parameter
If the RS does not synchronize its clock with the AS, it could be If the RS does not synchronize its clock with the AS, it could be
tricked into accepting old access tokens, that are either expired or tricked into accepting old access tokens that are either expired or
have been compromised. In order to ensure some level of token have been compromised. In order to ensure some level of token
freshness in that case, the RS can use the "cnonce" (client-nonce) freshness in that case, the RS can use the "cnonce" (client-nonce)
parameter. The processing requirements for this parameter are as parameter. The processing requirements for this parameter are as
follows: follows:
* An RS sending a "cnonce" parameter in an "AS Request Creation * An RS sending a "cnonce" parameter in an "AS Request Creation
Hints" message MUST store information to validate that a given Hints" message MUST store information to validate that a given
cnonce is fresh. How this is implemented internally is out of cnonce is fresh. How this is implemented internally is out of
scope for this specification. Expiration of client-nonces should scope for this specification. Expiration of client-nonces should
be based roughly on the time it would take a client to obtain an be based roughly on the time it would take a client to obtain an
skipping to change at page 20, line 11 skipping to change at line 902
* If an AS grants an access token request containing a "cnonce" * If an AS grants an access token request containing a "cnonce"
parameter, it MUST include this value in the access token, using parameter, it MUST include this value in the access token, using
the "cnonce" claim specified in Section 5.10. the "cnonce" claim specified in Section 5.10.
* An RS that is using the client-nonce mechanism and that receives * An RS that is using the client-nonce mechanism and that receives
an access token MUST verify that this token contains a cnonce an access token MUST verify that this token contains a cnonce
claim, with a client-nonce value that is fresh according to the claim, with a client-nonce value that is fresh according to the
information stored at the first step above. If the cnonce claim information stored at the first step above. If the cnonce claim
is not present or if the cnonce claim value is not fresh, the RS is not present or if the cnonce claim value is not fresh, the RS
MUST discard the access token. If this was an interaction with MUST discard the access token. If this was an interaction with
the authz-info endpoint the RS MUST also respond with an error the authz-info endpoint, the RS MUST also respond with an error
message using a response code equivalent to the CoAP code 4.01 message using a response code equivalent to the CoAP code 4.01
(Unauthorized). (Unauthorized).
5.4. Authorization Grants 5.4. Authorization Grants
To request an access token, the client obtains authorization from the To request an access token, the client obtains authorization from the
resource owner or uses its client credentials as a grant. The resource owner or uses its client credentials as a grant. The
authorization is expressed in the form of an authorization grant. authorization is expressed in the form of an authorization grant.
The OAuth framework [RFC6749] defines four grant types. The grant The OAuth framework [RFC6749] defines four grant types. The grant
types can be split up into two groups, those granted on behalf of the types can be split up into two groups: those granted on behalf of the
resource owner (password, authorization code, implicit) and those for resource owner (password, authorization code, implicit) and those for
the client (client credentials). Further grant types have been added the client (client credentials). Further grant types have been added
later, such as [RFC7521] defining an assertion-based authorization later, such as an assertion-based authorization grant defined in
grant. [RFC7521].
The grant type is selected depending on the use case. In cases where The grant type is selected depending on the use case. In cases where
the client acts on behalf of the resource owner, the authorization the client acts on behalf of the resource owner, the authorization
code grant is recommended. If the client acts on behalf of the code grant is recommended. If the client acts on behalf of the
resource owner, but does not have any display or has very limited resource owner but does not have any display or has very limited
interaction possibilities, it is recommended to use the device code interaction possibilities, it is recommended to use the device code
grant defined in [RFC8628]. In cases where the client acts grant defined in [RFC8628]. In cases where the client acts
autonomously the client credentials grant is recommended. autonomously, the client credentials grant is recommended.
For details on the different grant types, see section 1.3 of For details on the different grant types, see Section 1.3 of
[RFC6749]. The OAuth 2.0 framework provides an extension mechanism [RFC6749]. The OAuth 2.0 framework provides an extension mechanism
for defining additional grant types, so profiles of this framework for defining additional grant types, so profiles of this framework
MAY define additional grant types, if needed. MAY define additional grant types, if needed.
5.5. Client Credentials 5.5. Client Credentials
Authentication of the client is mandatory independent of the grant Authentication of the client is mandatory independent of the grant
type when requesting an access token from the token endpoint. In the type when requesting an access token from the token endpoint. In the
case of the client credentials grant type, the authentication and case of the client credentials grant type, the authentication and
grant coincide. grant coincide.
Client registration and provisioning of client credentials to the Client registration and provisioning of client credentials to the
client is out of scope for this specification. client is out of scope for this specification.
The OAuth framework defines one client credential type in section The OAuth framework defines two client credential types in
2.3.1 of [RFC6749]: client id and client secret. Section 2.3.1 of [RFC6749]: client id and client secret.
[I-D.erdtman-ace-rpcc] adds raw-public-key and pre-shared-key to the [OAUTH-RPCC] adds raw public key and pre-shared key to the client
client credentials types. Profiles of this framework MAY extend with credentials types. Profiles of this framework MAY extend with an
an additional client credentials type using client certificates. additional client credentials type using client certificates.
5.6. AS Authentication 5.6. AS Authentication
The client credential grant does not, by default, authenticate the AS The client credentials grant does not, by default, authenticate the
that the client connects to. In classic OAuth, the AS is AS that the client connects to. In classic OAuth, the AS is
authenticated with a TLS server certificate. authenticated with a TLS server certificate.
Profiles of this framework MUST specify how clients authenticate the Profiles of this framework MUST specify how clients authenticate the
AS and how communication security is implemented. By default, server AS and how communication security is implemented. By default, server
side TLS certificates, as defined by OAuth 2.0, are required. side TLS certificates, as defined by OAuth 2.0, are required.
5.7. The Authorization Endpoint 5.7. The Authorization Endpoint
The OAuth 2.0 authorization endpoint is used to interact with the The OAuth 2.0 authorization endpoint is used to interact with the
resource owner and obtain an authorization grant, in certain grant resource owner and obtain an authorization grant in certain grant
flows. The primary use case for the ACE-OAuth framework is for flows. The primary use case for the ACE-OAuth framework is for
machine-to-machine interactions that do not involve the resource machine-to-machine interactions that do not involve the resource
owner in the authorization flow; therefore, this endpoint is out of owner in the authorization flow; therefore, this endpoint is out of
scope here. Future profiles may define constrained adaptation scope here. Future profiles may define constrained adaptation
mechanisms for this endpoint as well. Non-constrained clients mechanisms for this endpoint as well. Nonconstrained clients
interacting with constrained resource servers can use the interacting with constrained resource servers can use the
specification in section 3.1 of [RFC6749] and the attack specification in Section 3.1 of [RFC6749] and the attack
countermeasures suggested in section 4.2 of [RFC6819]. countermeasures suggested in Section 4.2 of [RFC6819].
5.8. The Token Endpoint 5.8. The Token Endpoint
In standard OAuth 2.0, the AS provides the token endpoint for In standard OAuth 2.0, the AS provides the token endpoint for
submitting access token requests. This framework extends the submitting access token requests. This framework extends the
functionality of the token endpoint, giving the AS the possibility to functionality of the token endpoint, giving the AS the possibility to
help the client and RS to establish shared keys or to exchange their help the client and RS establish shared keys or exchange their public
public keys. Furthermore, this framework defines encodings using keys. Furthermore, this framework defines encodings using CBOR as a
CBOR, as a substitute for JSON. substitute for JSON.
The endpoint may also be exposed over HTTPS as in classical OAuth or The endpoint may also be exposed over HTTPS, as in classical OAuth or
even other transports. A profile MUST define the details of the even other transports. A profile MUST define the details of the
mapping between the fields described below, and these transports. If mapping between the fields described below and these transports. If
HTTPS is used, the semantics of Sections 4.1.3 and 4.1.4 of the OAuth HTTPS with JSON is used, the semantics of Sections 4.1.3 and 4.1.4 of
2.0 specification MUST be followed (with additions as described the OAuth 2.0 specification [RFC6749] MUST be followed (with
below). If the CoAP is some other transport with CBOR payload format additions as described below). If CBOR is used as the payload
is supported, the semantics described in this section MUST be format, the semantics described in this section MUST be followed.
followed.
For the AS to be able to issue a token, the client MUST be For the AS to be able to issue a token, the client MUST be
authenticated and present a valid grant for the scopes requested. authenticated and present a valid grant for the scopes requested.
Profiles of this framework MUST specify how the AS authenticates the Profiles of this framework MUST specify how the AS authenticates the
client and how the communication between client and AS is protected, client and how the communication between the client and AS is
fulfilling the requirements specified in Section 5. protected, fulfilling the requirements specified in Section 5.
The default name of this endpoint in an url-path SHOULD be '/token'. The default name of this endpoint in a url-path SHOULD be '/token'.
However, implementations are not required to use this name and can However, implementations are not required to use this name and can
define their own instead. define their own instead.
The figures of this section use CBOR diagnostic notation without the The figures of this section use CBOR diagnostic notation without the
integer abbreviations for the parameters or their values for integer abbreviations for the parameters or their values for
illustrative purposes. Note that implementations MUST use the illustrative purposes. Note that implementations MUST use the
integer abbreviations and the binary CBOR encoding, if the CBOR integer abbreviations and the binary CBOR encoding if the CBOR
encoding is used. encoding is used.
5.8.1. Client-to-AS Request 5.8.1. Client-to-AS Request
The client sends a POST request to the token endpoint at the AS. The The client sends a POST request to the token endpoint at the AS. The
profile MUST specify how the communication is protected. The content profile MUST specify how the communication is protected. The content
of the request consists of the parameters specified in the relevant of the request consists of the parameters specified in the relevant
subsection of section 4 of the OAuth 2.0 specification [RFC6749], subsection of Section 4 of the OAuth 2.0 specification [RFC6749],
depending on the grant type, with the following exceptions and depending on the grant type, with the following exceptions and
additions: additions:
* The parameter "grant_type" is OPTIONAL in the context of this * The parameter "grant_type" is OPTIONAL in the context of this
framework (as opposed to REQUIRED in RFC6749). If that parameter framework (as opposed to REQUIRED in [RFC6749]). If that
is missing, the default value "client_credentials" is implied. parameter is missing, the default value "client_credentials" is
implied.
* The "audience" parameter from [RFC8693] is OPTIONAL to request an * The "audience" parameter from [RFC8693] is OPTIONAL to request an
access token bound to a specific audience. access token bound to a specific audience.
* The "cnonce" parameter defined in Section 5.8.4.4 is REQUIRED if * The "cnonce" parameter defined in Section 5.8.4.4 is REQUIRED if
the RS provided a client-nonce in the "AS Request Creation Hints" the RS provided a client-nonce in the "AS Request Creation Hints"
message Section 5.3 message (Section 5.3).
* The "scope" parameter MAY be encoded as a byte string instead of * The "scope" parameter MAY be encoded as a byte string instead of
the string encoding specified in section 3.3 of [RFC6749], in the string encoding specified in Section 3.3 of [RFC6749] or in
order allow compact encoding of complex scopes. The syntax of order to allow compact encoding of complex scopes. The syntax of
such a binary encoding is explicitly not specified here and left such a binary encoding is explicitly not specified here and left
to profiles or applications. Note specifically that a binary to profiles or applications. Note specifically that a binary
encoded scope does not necessarily use the space character '0x20' encoded scope does not necessarily use the space character '0x20'
to delimit scope-tokens. to delimit scope-tokens.
* The client can send an empty (null value) "ace_profile" parameter * The client can send an empty (null value) "ace_profile" parameter
to indicate that it wants the AS to include the "ace_profile" to indicate that it wants the AS to include the "ace_profile"
parameter in the response. See Section 5.8.4.3. parameter in the response. See Section 5.8.4.3.
* A client MUST be able to use the parameters from * A client MUST be able to use the parameters from [RFC9201] in an
[I-D.ietf-ace-oauth-params] in an access token request to the access token request to the token endpoint, and the AS MUST be
token endpoint and the AS MUST be able to process these additional able to process these additional parameters.
parameters.
The default behavior, is that the AS generates a symmetric proof-of- The default behavior is that the AS generates a symmetric proof-of-
possession key for the client. In order to use an asymmetric key possession key for the client. In order to use an asymmetric key
pair or to re-use a key previously established with the RS, the pair or to reuse a key previously established with the RS, the client
client is supposed to use the "req_cnf" parameter from is supposed to use the "req_cnf" parameter from [RFC9201].
[I-D.ietf-ace-oauth-params].
If CoAP is used then these parameters MUST be provided in a CBOR map, If CoAP is used, then these parameters MUST be provided in a CBOR map
see Figure 12. (see Table 5).
When HTTP is used as a transport then the client makes a request to When HTTP is used as a transport, then the client makes a request to
the token endpoint, the parameters MUST be encoded as defined in the token endpoint; the parameters MUST be encoded as defined in
Appendix B of [RFC6749]. Appendix B of [RFC6749].
The following examples illustrate different types of requests for The following examples illustrate different types of requests for
proof-of-possession tokens. proof-of-possession tokens.
Figure 5 shows a request for a token with a symmetric proof-of- Figure 4 shows a request for a token with a symmetric proof-of-
possession key. The content is displayed in CBOR diagnostic possession key. The content is displayed in CBOR diagnostic
notation, without abbreviations for better readability. notation, without abbreviations for better readability.
Header: POST (Code=0.02) Header: POST (Code=0.02)
Uri-Host: "as.example.com" Uri-Host: "as.example.com"
Uri-Path: "token" Uri-Path: "token"
Content-Format: "application/ace+cbor" Content-Format: "application/ace+cbor"
Payload: Payload:
{ {
"client_id" : "myclient", "client_id" : "myclient",
"audience" : "tempSensor4711" "audience" : "tempSensor4711"
} }
Figure 5: Example request for an access token bound to a Figure 4: Example Request for an Access Token Bound to a
symmetric key. Symmetric Key
Figure 6 shows a request for a token with an asymmetric proof-of- Figure 5 shows a request for a token with an asymmetric proof-of-
possession key. Note that in this example OSCORE [RFC8613] is used possession key. Note that, in this example, OSCORE [RFC8613] is used
to provide object-security, therefore the Content-Format is to provide object-security; therefore, the Content-Format is
"application/oscore" wrapping the "application/ace+cbor" type "application/oscore" wrapping the "application/ace+cbor" type
content. The OSCORE option has a decoded interpretation appended in content. The OSCORE option has a decoded interpretation appended in
parentheses for the reader's convenience. Also note that in this parentheses for the reader's convenience. Also note that, in this
example the audience is implicitly known by both client and AS. example, the audience is implicitly known by both the client and AS.
Furthermore note that this example uses the "req_cnf" parameter from Furthermore, note that this example uses the "req_cnf" parameter from
[I-D.ietf-ace-oauth-params]. [RFC9201].
Header: POST (Code=0.02) Header: POST (Code=0.02)
Uri-Host: "as.example.com" Uri-Host: "as.example.com"
Uri-Path: "token" Uri-Path: "token"
OSCORE: 0x09, 0x05, 0x44, 0x6C OSCORE: 0x09, 0x05, 0x44, 0x6C
(h=0, k=1, n=001, partialIV= 0x05, kid=[0x44, 0x6C]) (h=0, k=1, n=001, partialIV= 0x05, kid=[0x44, 0x6C])
Content-Format: "application/oscore" Content-Format: "application/oscore"
Payload: Payload:
0x44025d1 ... (full payload omitted for brevity) ... 68b3825e 0x44025d1 ... (full payload omitted for brevity) ... 68b3825e
skipping to change at page 24, line 28 skipping to change at line 1106
"COSE_Key" : { "COSE_Key" : {
"kty" : "EC", "kty" : "EC",
"kid" : h'11', "kid" : h'11',
"crv" : "P-256", "crv" : "P-256",
"x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8', "x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
"y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4' "y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
} }
} }
} }
Figure 6: Example token request bound to an asymmetric key. Figure 5: Example Token Request Bound to an Asymmetric Key
Figure 7 shows a request for a token where a previously communicated Figure 6 shows a request for a token where a previously communicated
proof-of-possession key is only referenced using the "req_cnf" proof-of-possession key is only referenced using the "req_cnf"
parameter from [I-D.ietf-ace-oauth-params]. parameter from [RFC9201].
Header: POST (Code=0.02) Header: POST (Code=0.02)
Uri-Host: "as.example.com" Uri-Host: "as.example.com"
Uri-Path: "token" Uri-Path: "token"
Content-Format: "application/ace+cbor" Content-Format: "application/ace+cbor"
Payload: Payload:
{ {
"client_id" : "myclient", "client_id" : "myclient",
"audience" : "valve424", "audience" : "valve424",
"scope" : "read", "scope" : "read",
"req_cnf" : { "req_cnf" : {
"kid" : b64'6kg0dXJM13U' "kid" : b64'6kg0dXJM13U'
} }
} }
Figure 7: Example request for an access token bound to a key Figure 6: Example Request for an Access Token Bound to a Key
reference. Reference
Refresh tokens are typically not stored as securely as proof-of- Refresh tokens are typically not stored as securely as proof-of-
possession keys in requesting clients. Proof-of-possession based possession keys in requesting clients. Proof-of-possession-based
refresh token requests MUST NOT request different proof-of-possession refresh token requests MUST NOT request different proof-of-possession
keys or different audiences in token requests. Refresh token keys or different audiences in token requests. Refresh token
requests can only use to request access tokens bound to the same requests can only be used to request access tokens bound to the same
proof-of-possession key and the same audience as access tokens issued proof-of-possession key and the same audience as access tokens issued
in the initial token request. in the initial token request.
5.8.2. AS-to-Client Response 5.8.2. AS-to-Client Response
If the access token request has been successfully verified by the AS If the access token request has been successfully verified by the AS
and the client is authorized to obtain an access token corresponding and the client is authorized to obtain an access token corresponding
to its access token request, the AS sends a response with the to its access token request, the AS sends a response with the
response code equivalent to the CoAP response code 2.01 (Created). response code equivalent to the CoAP response code 2.01 (Created).
If client request was invalid, or not authorized, the AS returns an If the client request was invalid, or not authorized, the AS returns
error response as described in Section 5.8.3. an error response, as described in Section 5.8.3.
Note that the AS decides which token type and profile to use when Note that the AS decides which token type and profile to use when
issuing a successful response. It is assumed that the AS has prior issuing a successful response. It is assumed that the AS has prior
knowledge of the capabilities of the client and the RS (see knowledge of the capabilities of the client and the RS (see
Appendix D). This prior knowledge may, for example, be set by the Appendix D). This prior knowledge may, for example, be set by the
use of a dynamic client registration protocol exchange [RFC7591]. If use of a dynamic client registration protocol exchange [RFC7591]. If
the client has requested a specific proof-of-possession key using the the client has requested a specific proof-of-possession key using the
"req_cnf" parameter from [I-D.ietf-ace-oauth-params], this may also "req_cnf" parameter from [RFC9201], this may also influence which
influence which profile the AS selects, as it needs to support the profile the AS selects, as it needs to support the use of the key
use of the key type requested the client. type requested by the client.
The content of the successful reply is the Access Information. When The content of the successful reply is the Access Information. When
using CoAP, the payload MUST be encoded as a CBOR map, when using using CoAP, the payload MUST be encoded as a CBOR map; when using
HTTP the encoding is a JSON map as specified in section 5.1 of HTTP, the encoding is a JSON map, as specified in Section 5.1 of
[RFC6749]. In both cases the parameters specified in Section 5.1 of [RFC6749]. In both cases, the parameters specified in Section 5.1 of
[RFC6749] are used, with the following additions and changes: [RFC6749] are used, with the following additions and changes:
ace_profile: ace_profile:
OPTIONAL unless the request included an empty ace_profile This parameter is OPTIONAL unless the request included an empty
parameter in which case it is MANDATORY. This indicates the ace_profile parameter, in which case it is MANDATORY. This
profile that the client MUST use towards the RS. See indicates the profile that the client MUST use towards the RS.
Section 5.8.4.3 for the formatting of this parameter. If this See Section 5.8.4.3 for the formatting of this parameter. If
parameter is absent, the AS assumes that the client implicitly this parameter is absent, the AS assumes that the client
knows which profile to use towards the RS. implicitly knows which profile to use towards the RS.
token_type: token_type:
This parameter is OPTIONAL, as opposed to 'required' in [RFC6749]. This parameter is OPTIONAL, as opposed to REQUIRED in
By default implementations of this framework SHOULD assume that [RFC6749]. By default, implementations of this framework
the token_type is "PoP". If a specific use case requires another SHOULD assume that the token_type is "PoP". If a specific use
token_type (e.g., "Bearer") to be used then this parameter is case requires another token_type (e.g., "Bearer") to be used,
REQUIRED. then this parameter is REQUIRED.
Furthermore [I-D.ietf-ace-oauth-params] defines additional parameters Furthermore, [RFC9201] defines additional parameters that the AS MUST
that the AS MUST be able to use when responding to a request to the be able to use when responding to a request to the token endpoint.
token endpoint.
Figure 8 summarizes the parameters that can currently be part of the Table 2 summarizes the parameters that can currently be part of the
Access Information. Future extensions may define additional Access Information. Future extensions may define additional
parameters. parameters.
/-------------------+-------------------------------\ +===================+==============+
| Parameter name | Specified in | | Parameter name | Specified in |
|-------------------+-------------------------------| +===================+==============+
| access_token | RFC 6749 | | access_token | [RFC6749] |
| token_type | RFC 6749 | +-------------------+--------------+
| expires_in | RFC 6749 | | token_type | [RFC6749] |
| refresh_token | RFC 6749 | +-------------------+--------------+
| scope | RFC 6749 | | expires_in | [RFC6749] |
| state | RFC 6749 | +-------------------+--------------+
| error | RFC 6749 | | refresh_token | [RFC6749] |
| error_description | RFC 6749 | +-------------------+--------------+
| error_uri | RFC 6749 | | scope | [RFC6749] |
| ace_profile | [this document] | +-------------------+--------------+
| cnf | [I-D.ietf-ace-oauth-params] | | state | [RFC6749] |
| rs_cnf | [I-D.ietf-ace-oauth-params] | +-------------------+--------------+
\-------------------+-------------------------------/ | error | [RFC6749] |
+-------------------+--------------+
| error_description | [RFC6749] |
+-------------------+--------------+
| error_uri | [RFC6749] |
+-------------------+--------------+
| ace_profile | RFC 9200 |
+-------------------+--------------+
| cnf | [RFC9201] |
+-------------------+--------------+
| rs_cnf | [RFC9201] |
+-------------------+--------------+
Figure 8: Access Information parameters Table 2: Access Information
Parameters
Figure 9 shows a response containing a token and a "cnf" parameter Figure 7 shows a response containing a token and a "cnf" parameter
with a symmetric proof-of-possession key, which is defined in with a symmetric proof-of-possession key, which is defined in
[I-D.ietf-ace-oauth-params]. Note that the key identifier 'kid' is [RFC9201]. Note that the key identifier 'kid' is only used to
only used to simplify indexing and retrieving the key, and no simplify indexing and retrieving the key, and no assumptions should
assumptions should be made that it is unique in the domains of either be made that it is unique in the domains of either the client or the
the client or the RS. RS.
Header: Created (Code=2.01) Header: Created (Code=2.01)
Content-Format: "application/ace+cbor" Content-Format: "application/ace+cbor"
Payload: Payload:
{ {
"access_token" : b64'SlAV32hkKG ... "access_token" : b64'SlAV32hkKG ...
(remainder of CWT omitted for brevity; (remainder of CWT omitted for brevity;
CWT contains COSE_Key in the "cnf" claim)', CWT contains COSE_Key in the "cnf" claim)',
"ace_profile" : "coap_dtls", "ace_profile" : "coap_dtls",
"expires_in" : "3600", "expires_in" : "3600",
"cnf" : { "cnf" : {
"COSE_Key" : { "COSE_Key" : {
"kty" : "Symmetric", "kty" : "Symmetric",
"kid" : b64'39Gqlw', "kid" : b64'39Gqlw',
"k" : b64'hJtXhkV8FJG+Onbc6mxCcQh' "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh'
} }
} }
} }
Figure 9: Example AS response with an access token bound to a Figure 7: Example AS Response with an Access Token Bound to a
symmetric key. Symmetric Key
5.8.3. Error Response 5.8.3. Error Response
The error responses for interactions with the AS are generally The error responses for interactions with the AS are generally
equivalent to the ones defined in Section 5.2 of [RFC6749], with the equivalent to the ones defined in Section 5.2 of [RFC6749], with the
following exceptions: following exceptions:
* When using CoAP the payload MUST be encoded as a CBOR map, with * When using CoAP, the payload MUST be encoded as a CBOR map, with
the Content-Format "application/ace+cbor". When using HTTP the the Content-Format "application/ace+cbor". When using HTTP, the
payload is encoded in JSON as specified in section 5.2 of payload is encoded in JSON, as specified in Section 5.2 of
[RFC6749]. [RFC6749].
* A response code equivalent to the CoAP code 4.00 (Bad Request) * A response code equivalent to the CoAP code 4.00 (Bad Request)
MUST be used for all error responses, except for invalid_client MUST be used for all error responses, except for invalid_client,
where a response code equivalent to the CoAP code 4.01 where a response code equivalent to the CoAP code 4.01
(Unauthorized) MAY be used under the same conditions as specified (Unauthorized) MAY be used under the same conditions as specified
in Section 5.2 of [RFC6749]. in Section 5.2 of [RFC6749].
* The parameters "error", "error_description" and "error_uri" MUST * The parameters "error", "error_description", and "error_uri" MUST
be abbreviated using the codes specified in Figure 12, when a CBOR be abbreviated using the codes specified in Table 5, when a CBOR
encoding is used. encoding is used.
* The error code (i.e., value of the "error" parameter) MUST be * The error code (i.e., value of the "error" parameter) MUST be
abbreviated as specified in Figure 10, when a CBOR encoding is abbreviated, as specified in Table 3, when a CBOR encoding is
used. used.
/---------------------------+--------+--------------------------\ +===========================+=============+========================+
| | CBOR | Original | | Name | CBOR Values | Original Specification |
| Name | Values | Specification | +===========================+=============+========================+
|---------------------------+--------+--------------------------| | invalid_request | 1 | Section 5.2 of |
| invalid_request | 1 | section 5.2 of [RFC6749] | | | | [RFC6749] |
| invalid_client | 2 | section 5.2 of [RFC6749] | +---------------------------+-------------+------------------------+
| invalid_grant | 3 | section 5.2 of [RFC6749] | | invalid_client | 2 | Section 5.2 of |
| unauthorized_client | 4 | section 5.2 of [RFC6749] | | | | [RFC6749] |
| unsupported_grant_type | 5 | section 5.2 of [RFC6749] | +---------------------------+-------------+------------------------+
| invalid_scope | 6 | section 5.2 of [RFC6749] | | invalid_grant | 3 | Section 5.2 of |
| unsupported_pop_key | 7 | [this document] | | | | [RFC6749] |
| incompatible_ace_profiles | 8 | [this document] | +---------------------------+-------------+------------------------+
\---------------------------+--------+--------------------------/ | unauthorized_client | 4 | Section 5.2 of |
| | | [RFC6749] |
+---------------------------+-------------+------------------------+
| unsupported_grant_type | 5 | Section 5.2 of |
| | | [RFC6749] |
+---------------------------+-------------+------------------------+
| invalid_scope | 6 | Section 5.2 of |
| | | [RFC6749] |
+---------------------------+-------------+------------------------+
| unsupported_pop_key | 7 | RFC 9200 |
+---------------------------+-------------+------------------------+
| incompatible_ace_profiles | 8 | RFC 9200 |
+---------------------------+-------------+------------------------+
Figure 10: CBOR abbreviations for common error codes Table 3: CBOR Abbreviations for Common Error Codes
In addition to the error responses defined in OAuth 2.0, the In addition to the error responses defined in OAuth 2.0, the
following behavior MUST be implemented by the AS: following behavior MUST be implemented by the AS:
* If the client submits an asymmetric key in the token request that * If the client submits an asymmetric key in the token request that
the RS cannot process, the AS MUST reject that request with a the RS cannot process, the AS MUST reject that request with a
response code equivalent to the CoAP code 4.00 (Bad Request) response code equivalent to the CoAP code 4.00 (Bad Request),
including the error code "unsupported_pop_key" specified in including the error code "unsupported_pop_key" specified in
Figure 10. Table 3.
* If the client and the RS it has requested an access token for do * If the client and the RS it has requested an access token for do
not share a common profile, the AS MUST reject that request with a not share a common profile, the AS MUST reject that request with a
response code equivalent to the CoAP code 4.00 (Bad Request) response code equivalent to the CoAP code 4.00 (Bad Request),
including the error code "incompatible_ace_profiles" specified in including the error code "incompatible_ace_profiles" specified in
Figure 10. Table 3.
5.8.4. Request and Response Parameters 5.8.4. Request and Response Parameters
This section provides more detail about the new parameters that can This section provides more detail about the new parameters that can
be used in access token requests and responses, as well as be used in access token requests and responses, as well as
abbreviations for more compact encoding of existing parameters and abbreviations for more compact encoding of existing parameters and
common parameter values. common parameter values.
5.8.4.1. Grant Type 5.8.4.1. Grant Type
The abbreviations specified in the registry defined in Section 8.5 The abbreviations specified in the registry defined in Section 8.5
MUST be used in CBOR encodings instead of the string values defined MUST be used in CBOR encodings instead of the string values defined
in [RFC6749], if CBOR payloads are used. in [RFC6749] if CBOR payloads are used.
/--------------------+------------+------------------------\ +====================+============+============================+
| Name | CBOR Value | Original Specification | | Name | CBOR Value | Original Specification |
|--------------------+------------+------------------------| +====================+============+============================+
| password | 0 | s. 4.3.2 of [RFC6749] | | password | 0 | Section 4.3.2 of [RFC6749] |
| authorization_code | 1 | s. 4.1.3 of [RFC6749] | +--------------------+------------+----------------------------+
| client_credentials | 2 | s. 4.4.2 of [RFC6749] | | authorization_code | 1 | Section 4.1.3 of [RFC6749] |
| refresh_token | 3 | s. 6 of [RFC6749] | +--------------------+------------+----------------------------+
\--------------------+------------+------------------------/ | client_credentials | 2 | Section 4.4.2 of [RFC6749] |
+--------------------+------------+----------------------------+
| refresh_token | 3 | Section 6 of [RFC6749] |
+--------------------+------------+----------------------------+
Figure 11: CBOR abbreviations for common grant types Table 4: CBOR Abbreviations for Common Grant Types
5.8.4.2. Token Type 5.8.4.2. Token Type
The "token_type" parameter, defined in section 5.1 of [RFC6749], The "token_type" parameter, defined in Section 5.1 of [RFC6749],
allows the AS to indicate to the client which type of access token it allows the AS to indicate to the client which type of access token it
is receiving (e.g., a bearer token). is receiving (e.g., a bearer token).
This document registers the new value "PoP" for the OAuth Access This document registers the new value "PoP" for the "OAuth Access
Token Types registry, specifying a proof-of-possession token. How Token Types" registry, specifying a proof-of-possession token. How
the proof-of-possession by the client to the RS is performed MUST be the proof of possession by the client to the RS is performed MUST be
specified by the profiles. specified by the profiles.
The values in the "token_type" parameter MUST use the CBOR The values in the "token_type" parameter MUST use the CBOR
abbreviations defined in the registry specified by Section 8.7, if a abbreviations defined in the registry specified by Section 8.7 if a
CBOR encoding is used. CBOR encoding is used.
In this framework the "pop" value for the "token_type" parameter is In this framework, the "pop" value for the "token_type" parameter is
the default. The AS may, however, provide a different value from the default. The AS may, however, provide a different value from
those registered in [IANA.OAuthAccessTokenTypes]. those registered in [IANA.OAuthAccessTokenTypes].
5.8.4.3. Profile 5.8.4.3. Profile
Profiles of this framework MUST define the communication protocol and Profiles of this framework MUST define the communication protocol and
the communication security protocol between the client and the RS. the communication security protocol between the client and the RS.
The security protocol MUST provide encryption, integrity and replay The security protocol MUST provide encryption, integrity, and replay
protection. It MUST also provide a binding between requests and protection. It MUST also provide a binding between requests and
responses. Furthermore profiles MUST define a list of allowed proof- responses. Furthermore, profiles MUST define a list of allowed
of-possession methods, if they support proof-of-possession tokens. proof-of-possession methods if they support proof-of-possession
tokens.
A profile MUST specify an identifier that MUST be used to uniquely A profile MUST specify an identifier that MUST be used to uniquely
identify itself in the "ace_profile" parameter. The textual identify itself in the "ace_profile" parameter. The textual
representation of the profile identifier is intended for human representation of the profile identifier is intended for human
readability and for JSON-based interactions, it MUST NOT be used for readability and for JSON-based interactions; it MUST NOT be used for
CBOR-based interactions. Profiles MUST register their identifier in CBOR-based interactions. Profiles MUST register their identifier in
the registry defined in Section 8.8. the registry defined in Section 8.8.
Profiles MAY define additional parameters for both the token request Profiles MAY define additional parameters for both the token request
and the Access Information in the access token response in order to and the Access Information in the access token response in order to
support negotiation or signaling of profile specific parameters. support negotiation or signaling of profile-specific parameters.
Clients that want the AS to provide them with the "ace_profile" Clients that want the AS to provide them with the "ace_profile"
parameter in the access token response can indicate that by sending a parameter in the access token response can indicate that by sending a
ace_profile parameter with a null value for CBOR-based interactions, ace_profile parameter with a null value for CBOR-based interactions,
or an empty string if CBOR is not used, in the access token request. or an empty string if CBOR is not used, in the access token request.
5.8.4.4. Client-Nonce 5.8.4.4. Client-Nonce
This parameter MUST be sent from the client to the AS, if it This parameter MUST be sent from the client to the AS if it
previously received a "cnonce" parameter in the "AS Request Creation previously received a "cnonce" parameter in the "AS Request Creation
Hints" Section 5.3. The parameter is encoded as a byte string for Hints" (Section 5.3). The parameter is encoded as a byte string for
CBOR-based interactions, and as a string (Base64 encoded binary) if CBOR-based interactions and as a string (base64url without padding
CBOR is not used. It MUST copy the value from the cnonce parameter encoded binary [RFC4648]) if CBOR is not used. It MUST copy the
in the "AS Request Creation Hints". value from the cnonce parameter in the "AS Request Creation Hints".
5.8.5. Mapping Parameters to CBOR 5.8.5. Mapping Parameters to CBOR
If CBOR encoding is used, all OAuth parameters in access token If CBOR encoding is used, all OAuth parameters in access token
requests and responses MUST be mapped to CBOR types as specified in requests and responses MUST be mapped to CBOR types, as specified in
the registry defined by Section 8.10, using the given integer the registry defined by Section 8.10, using the given integer
abbreviation for the map keys. abbreviation for the map keys.
Note that we have aligned the abbreviations corresponding to claims Note that we have aligned the abbreviations corresponding to claims
with the abbreviations defined in [RFC8392]. with the abbreviations defined in [RFC8392].
Note also that abbreviations from -24 to 23 have a 1 byte encoding Note also that abbreviations from -24 to 23 have a 1-byte encoding
size in CBOR. We have thus chosen to assign abbreviations in that size in CBOR. We have thus chosen to assign abbreviations in that
range to parameters we expect to be used most frequently in range to parameters we expect to be used most frequently in
constrained scenarios. constrained scenarios.
/-------------------+----------+---------------------+---------------\ +===================+==========+=============+===============+
| | | | Original | | Name | CBOR Key | Value Type | Original |
| Name | CBOR Key | Value Type | Specification | | | | | Specification |
|-------------------+----------+---------------------+---------------| +===================+==========+=============+===============+
| access_token | 1 | byte string | [RFC6749] | | access_token | 1 | byte string | [RFC6749] |
| expires_in | 2 | unsigned integer | [RFC6749] | +-------------------+----------+-------------+---------------+
| audience | 5 | text string | [RFC8693] | | expires_in | 2 | unsigned | [RFC6749] |
| scope | 9 | text or byte string | [RFC6749] | | | | integer | |
| client_id | 24 | text string | [RFC6749] | +-------------------+----------+-------------+---------------+
| client_secret | 25 | byte string | [RFC6749] | | audience | 5 | text string | [RFC8693] |
| response_type | 26 | text string | [RFC6749] | +-------------------+----------+-------------+---------------+
| redirect_uri | 27 | text string | [RFC6749] | | scope | 9 | text or | [RFC6749] |
| state | 28 | text string | [RFC6749] | | | | byte string | |
| code | 29 | byte string | [RFC6749] | +-------------------+----------+-------------+---------------+
| error | 30 | integer | [RFC6749] | | client_id | 24 | text string | [RFC6749] |
| error_description | 31 | text string | [RFC6749] | +-------------------+----------+-------------+---------------+
| error_uri | 32 | text string | [RFC6749] | | client_secret | 25 | byte string | [RFC6749] |
| grant_type | 33 | unsigned integer | [RFC6749] | +-------------------+----------+-------------+---------------+
| token_type | 34 | integer | [RFC6749] | | response_type | 26 | text string | [RFC6749] |
| username | 35 | text string | [RFC6749] | +-------------------+----------+-------------+---------------+
| password | 36 | text string | [RFC6749] | | redirect_uri | 27 | text string | [RFC6749] |
| refresh_token | 37 | byte string | [RFC6749] | +-------------------+----------+-------------+---------------+
| ace_profile | 38 | integer |[this document]| | state | 28 | text string | [RFC6749] |
| cnonce | 39 | byte string |[this document]| +-------------------+----------+-------------+---------------+
\-------------------+----------+---------------------+---------------/ | code | 29 | byte string | [RFC6749] |
+-------------------+----------+-------------+---------------+
| error | 30 | integer | [RFC6749] |
+-------------------+----------+-------------+---------------+
| error_description | 31 | text string | [RFC6749] |
+-------------------+----------+-------------+---------------+
| error_uri | 32 | text string | [RFC6749] |
+-------------------+----------+-------------+---------------+
| grant_type | 33 | unsigned | [RFC6749] |
| | | integer | |
+-------------------+----------+-------------+---------------+
| token_type | 34 | integer | [RFC6749] |
+-------------------+----------+-------------+---------------+
| username | 35 | text string | [RFC6749] |
+-------------------+----------+-------------+---------------+
| password | 36 | text string | [RFC6749] |
+-------------------+----------+-------------+---------------+
| refresh_token | 37 | byte string | [RFC6749] |
+-------------------+----------+-------------+---------------+
| ace_profile | 38 | integer | RFC 9200 |
+-------------------+----------+-------------+---------------+
| cnonce | 39 | byte string | RFC 9200 |
+-------------------+----------+-------------+---------------+
Figure 12: CBOR mappings used in token requests and responses Table 5: CBOR Mappings Used in Token Requests and Responses
5.9. The Introspection Endpoint 5.9. The Introspection Endpoint
Token introspection [RFC7662] MAY be implemented by the AS, and the Token introspection [RFC7662] MAY be implemented by the AS and the
RS. When implemented, it MAY be used by the RS and to query the AS RS. When implemented, it MAY be used by the RS and to query the AS
for metadata about a given token, e.g., validity or scope. Analogous for metadata about a given token, e.g., validity or scope. Analogous
to the protocol defined in [RFC7662] for HTTP and JSON, this section to the protocol defined in [RFC7662] for HTTP and JSON, this section
defines adaptations to more constrained environments using CBOR and defines adaptations to more constrained environments using CBOR and
leaving the choice of the application protocol to the profile. leaving the choice of the application protocol to the profile.
Communication between the requesting entity and the introspection Communication between the requesting entity and the introspection
endpoint at the AS MUST be integrity protected and encrypted. The endpoint at the AS MUST be integrity protected and encrypted. The
communication security protocol MUST also provide a binding between communication security protocol MUST also provide a binding between
requests and responses. Furthermore, the two interacting parties requests and responses. Furthermore, the two interacting parties
MUST perform mutual authentication. Finally, the AS SHOULD verify MUST perform mutual authentication. Finally, the AS SHOULD verify
that the requesting entity has the right to access introspection that the requesting entity has the right to access introspection
information about the provided token. Profiles of this framework information about the provided token. Profiles of this framework
that support introspection MUST specify how authentication and that support introspection MUST specify how authentication and
communication security between the requesting entity and the AS is communication security between the requesting entity and the AS is
implemented. implemented.
The default name of this endpoint in an url-path SHOULD be The default name of this endpoint in a url-path SHOULD be
'/introspect'. However, implementations are not required to use this '/introspect'. However, implementations are not required to use this
name and can define their own instead. name and can define their own instead.
The figures of this section use the CBOR diagnostic notation without The figures of this section use the CBOR diagnostic notation without
the integer abbreviations for the parameters and their values for the integer abbreviations for the parameters and their values for
better readability. better readability.
5.9.1. Introspection Request 5.9.1. Introspection Request
The requesting entity sends a POST request to the introspection The requesting entity sends a POST request to the introspection
endpoint at the AS. The profile MUST specify how the communication endpoint at the AS. The profile MUST specify how the communication
is protected. If CoAP is used, the payload MUST be encoded as a CBOR is protected. If CoAP is used, the payload MUST be encoded as a CBOR
map with a "token" entry containing the access token. Further map with a "token" entry containing the access token. Further
optional parameters representing additional context that is known by optional parameters representing additional context that is known by
the requesting entity to aid the AS in its response MAY be included. the requesting entity to aid the AS in its response MAY be included.
For CoAP-based interaction, all messages MUST use the content type For CoAP-based interaction, all messages MUST use the content type
"application/ace+cbor". For HTTP the encoding defined in section 2.1 "application/ace+cbor". For HTTP, the encoding defined in
of [RFC7662] is used. Section 2.1 of [RFC7662] is used.
The same parameters are required and optional as in Section 2.1 of The same parameters are required and optional as in Section 2.1 of
[RFC7662]. [RFC7662].
For example, Figure 13 shows an RS calling the token introspection For example, Figure 8 shows an RS calling the token introspection
endpoint at the AS to query about an OAuth 2.0 proof-of-possession endpoint at the AS to query about an OAuth 2.0 proof-of-possession
token. Note that object security based on OSCORE [RFC8613] is token. Note that object security based on OSCORE [RFC8613] is
assumed in this example, therefore the Content-Format is assumed in this example; therefore, the Content-Format is
"application/oscore". Figure 14 shows the decoded payload. "application/oscore". Figure 9 shows the decoded payload.
Header: POST (Code=0.02) Header: POST (Code=0.02)
Uri-Host: "as.example.com" Uri-Host: "as.example.com"
Uri-Path: "introspect" Uri-Path: "introspect"
OSCORE: 0x09, 0x05, 0x25 OSCORE: 0x09, 0x05, 0x25
Content-Format: "application/oscore" Content-Format: "application/oscore"
Payload: Payload:
... COSE content ... ... COSE content ...
Figure 13: Example introspection request. Figure 8: Example Introspection Request
{ {
"token" : b64'7gj0dXJQ43U', "token" : b64'7gj0dXJQ43U',
"token_type_hint" : "PoP" "token_type_hint" : "PoP"
} }
Figure 14: Decoded payload. Figure 9: Decoded Payload
5.9.2. Introspection Response 5.9.2. Introspection Response
If the introspection request is authorized and successfully If the introspection request is authorized and successfully
processed, the AS sends a response with the response code equivalent processed, the AS sends a response with the response code equivalent
to the CoAP code 2.01 (Created). If the introspection request was to the CoAP code 2.01 (Created). If the introspection request was
invalid, not authorized or couldn't be processed the AS returns an invalid, not authorized, or couldn't be processed, the AS returns an
error response as described in Section 5.9.3. error response, as described in Section 5.9.3.
In a successful response, the AS encodes the response parameters in a In a successful response, the AS encodes the response parameters in a
map. If CoAP is used, this MUST be encoded as a CBOR map, if HTTP is map. If CoAP is used, this MUST be encoded as a CBOR map; if HTTP is
used the JSON encoding specified in section 2.2 of [RFC7662] is used. used, the JSON encoding specified in Section 2.2 of [RFC7662] is
The map containing the response payload includes the same required used. The map containing the response payload includes the same
and optional parameters as in Section 2.2 of [RFC7662] with the required and optional parameters as in Section 2.2 of [RFC7662], with
following additions: the following additions:
ace_profile OPTIONAL. This indicates the profile that the RS MUST ace_profile:
use with the client. See Section 5.8.4.3 for more details on the This parameter is OPTIONAL. This indicates the profile that the
formatting of this parameter. If this parameter is absent, the AS RS MUST use with the client. See Section 5.8.4.3 for more details
assumes that the RS implicitly knows which profile to use towards on the formatting of this parameter. If this parameter is absent,
the client. the AS assumes that the RS implicitly knows which profile to use
towards the client.
cnonce OPTIONAL. A client-nonce provided to the AS by the client. cnonce:
The RS MUST verify that this corresponds to the client-nonce This parameter is OPTIONAL. This is a client-nonce provided to
previously provided to the client in the "AS Request Creation the AS by the client. The RS MUST verify that this corresponds to
Hints". See Section 5.3 and Section 5.8.4.4. the client-nonce previously provided to the client in the "AS
Request Creation Hints". See Sections 5.3 and 5.8.4.4. Its value
is a byte string when encoded in CBOR and is the base64url
encoding of this byte string without padding when encoded in JSON
[RFC4648].
cti OPTIONAL. The "cti" claim associated to this access token. cti:
This parameter has the same meaning and processing rules as the This parameter is OPTIONAL. This is the "cti" claim associated to
"jti" parameter defined in section 3.1.2 of [RFC7662] except that this access token. This parameter has the same meaning and
the value is a byte string. processing rules as the "jti" parameter defined in Section 3.1.2
of [RFC7662] except that its value is a byte string when encoded
in CBOR and is the base64url encoding of this byte string without
padding when encoded in JSON [RFC4648].
exi OPTIONAL. The "expires-in" claim associated to this access exi:
token. See Section 5.10.3. This parameter is OPTIONAL. This is the "expires-in" claim
associated to this access token. See Section 5.10.3.
Furthermore [I-D.ietf-ace-oauth-params] defines more parameters that Furthermore, [RFC9201] defines more parameters that the AS MUST be
the AS MUST be able to use when responding to a request to the able to use when responding to a request to the introspection
introspection endpoint. endpoint.
For example, Figure 15 shows an AS response to the introspection For example, Figure 10 shows an AS response to the introspection
request in Figure 13. Note that this example contains the "cnf" request in Figure 8. Note that this example contains the "cnf"
parameter defined in [I-D.ietf-ace-oauth-params]. parameter defined in [RFC9201].
Header: Created (Code=2.01) Header: Created (Code=2.01)
Content-Format: "application/ace+cbor" Content-Format: "application/ace+cbor"
Payload: Payload:
{ {
"active" : true, "active" : true,
"scope" : "read", "scope" : "read",
"ace_profile" : "coap_dtls", "ace_profile" : "coap_dtls",
"cnf" : { "cnf" : {
"COSE_Key" : { "COSE_Key" : {
"kty" : "Symmetric", "kty" : "Symmetric",
"kid" : b64'39Gqlw', "kid" : b64'39Gqlw',
"k" : b64'hJtXhkV8FJG+Onbc6mxCcQh' "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh'
} }
} }
} }
Figure 15: Example introspection response. Figure 10: Example Introspection Response
5.9.3. Error Response 5.9.3. Error Response
The error responses for CoAP-based interactions with the AS are The error responses for CoAP-based interactions with the AS are
equivalent to the ones for HTTP-based interactions as defined in equivalent to the ones for HTTP-based interactions, as defined in
Section 2.3 of [RFC7662], with the following differences: Section 2.3 of [RFC7662], with the following differences:
* If content is sent and CoAP is used the payload MUST be encoded as * If content is sent and CoAP is used, the payload MUST be encoded
a CBOR map and the Content-Format "application/ace+cbor" MUST be as a CBOR map and the Content-Format "application/ace+cbor" MUST
used. For HTTP the encoding defined in section 2.3 of [RFC6749] be used. For HTTP, the encoding defined in Section 2.3 of
is used. [RFC6749] is used.
* If the credentials used by the requesting entity (usually the RS) * If the credentials used by the requesting entity (usually the RS)
are invalid the AS MUST respond with the response code equivalent are invalid, the AS MUST respond with the response code equivalent
to the CoAP code 4.01 (Unauthorized) and use the required and to the CoAP code 4.01 (Unauthorized) and use the required and
optional parameters from Section 2.3 in [RFC7662]. optional parameters from Section 2.3 of [RFC7662].
* If the requesting entity does not have the right to perform this * If the requesting entity does not have the right to perform this
introspection request, the AS MUST respond with a response code introspection request, the AS MUST respond with a response code
equivalent to the CoAP code 4.03 (Forbidden). In this case no equivalent to the CoAP code 4.03 (Forbidden). In this case, no
payload is returned. payload is returned.
* The parameters "error", "error_description" and "error_uri" MUST * The parameters "error", "error_description", and "error_uri" MUST
be abbreviated using the codes specified in Figure 12. be abbreviated using the codes specified in Table 5.
* The error codes MUST be abbreviated using the codes specified in * The error codes MUST be abbreviated using the codes specified in
the registry defined by Section 8.4. the registry defined by Section 8.4.
Note that a properly formed and authorized query for an inactive or Note that a properly formed and authorized query for an inactive or
otherwise invalid token does not warrant an error response by this otherwise invalid token does not warrant an error response by this
specification. In these cases, the authorization server MUST instead specification. In these cases, the authorization server MUST instead
respond with an introspection response with the "active" field set to respond with an introspection response with the "active" field set to
"false". "false".
5.9.4. Mapping Introspection Parameters to CBOR 5.9.4. Mapping Introspection Parameters to CBOR
If CBOR is used, the introspection request and response parameters If CBOR is used, the introspection request and response parameters
MUST be mapped to CBOR types as specified in the registry defined by MUST be mapped to CBOR types, as specified in the registry defined by
Section 8.12, using the given integer abbreviation for the map key. Section 8.12, using the given integer abbreviation for the map key.
Note that we have aligned abbreviations that correspond to a claim Note that we have aligned abbreviations that correspond to a claim
with the abbreviations defined in [RFC8392] and the abbreviations of with the abbreviations defined in [RFC8392] and the abbreviations of
parameters with the same name from Section 5.8.5. parameters with the same name from Section 5.8.5.
/-------------------+----------+-------------------+---------------\ +===================+======+======================+===============+
| | | | Original | | Parameter name | CBOR | Value Type | Original |
| Parameter name | CBOR Key | Value Type | Specification | | | Key | | Specification |
|-------------------+----------+-------------------+---------------| +===================+======+======================+===============+
| iss | 1 | text string | [RFC7662] | | iss | 1 | text string | [RFC7662] |
| sub | 2 | text string | [RFC7662] | +-------------------+------+----------------------+---------------+
| aud | 3 | text string | [RFC7662] | | sub | 2 | text string | [RFC7662] |
| exp | 4 | integer or | [RFC7662] | +-------------------+------+----------------------+---------------+
| | | floating-point | | | aud | 3 | text string | [RFC7662] |
| | | number | | +-------------------+------+----------------------+---------------+
| nbf | 5 | integer or | [RFC7662] | | exp | 4 | integer or floating- | [RFC7662] |
| | | floating-point | | | | | point number | |
| | | number | | +-------------------+------+----------------------+---------------+
| iat | 6 | integer or | [RFC7662] | | nbf | 5 | integer or floating- | [RFC7662] |
| | | floating-point | | | | | point number | |
| | | number | | +-------------------+------+----------------------+---------------+
| cti | 7 | byte string |[this document]| | iat | 6 | integer or floating- | [RFC7662] |
| scope | 9 | text or | [RFC7662] | | | | point number | |
| | | byte string | | +-------------------+------+----------------------+---------------+
| active | 10 | True or False | [RFC7662] | | cti | 7 | byte string | RFC 9200 |
| token | 11 | byte string | [RFC7662] | +-------------------+------+----------------------+---------------+
| client_id | 24 | text string | [RFC7662] | | scope | 9 | text or byte string | [RFC7662] |
| error | 30 | integer | [RFC7662] | +-------------------+------+----------------------+---------------+
| error_description | 31 | text string | [RFC7662] | | active | 10 | True or False | [RFC7662] |
| error_uri | 32 | text string | [RFC7662] | +-------------------+------+----------------------+---------------+
| token_type_hint | 33 | text string | [RFC7662] | | token | 11 | byte string | [RFC7662] |
| token_type | 34 | integer | [RFC7662] | +-------------------+------+----------------------+---------------+
| username | 35 | text string | [RFC7662] | | client_id | 24 | text string | [RFC7662] |
| ace_profile | 38 | integer |[this document]| +-------------------+------+----------------------+---------------+
| cnonce | 39 | byte string |[this document]| | error | 30 | integer | [RFC7662] |
| exi | 40 | unsigned integer |[this document]| +-------------------+------+----------------------+---------------+
\-------------------+----------+-------------------+---------------/ | error_description | 31 | text string | [RFC7662] |
Figure 16: CBOR mappings for Token Introspection Parameters. +-------------------+------+----------------------+---------------+
| error_uri | 32 | text string | [RFC7662] |
+-------------------+------+----------------------+---------------+
| token_type_hint | 33 | text string | [RFC7662] |
+-------------------+------+----------------------+---------------+
| token_type | 34 | integer | [RFC7662] |
+-------------------+------+----------------------+---------------+
| username | 35 | text string | [RFC7662] |
+-------------------+------+----------------------+---------------+
| ace_profile | 38 | integer | RFC 9200 |
+-------------------+------+----------------------+---------------+
| cnonce | 39 | byte string | RFC 9200 |
+-------------------+------+----------------------+---------------+
| exi | 40 | integer | RFC 9200 |
+-------------------+------+----------------------+---------------+
Table 6: CBOR Mappings for Token Introspection Parameters
5.10. The Access Token 5.10. The Access Token
In this framework the use of CBOR Web Token (CWT) as specified in In this framework, the use of CBOR Web Token (CWT) as specified in
[RFC8392] is RECOMMENDED. [RFC8392] is RECOMMENDED.
In order to facilitate offline processing of access tokens, this In order to facilitate offline processing of access tokens, this
document uses the "cnf" claim from [RFC8747] and the "scope" claim document uses the "cnf" claim from [RFC8747] and the "scope" claim
from [RFC8693] for JWT- and CWT-encoded tokens. In addition to from [RFC8693] for JWT- and CWT-encoded tokens. In addition to
string encoding specified for the "scope" claim, a binary encoding string encoding specified for the "scope" claim, a binary encoding
MAY be used. The syntax of such an encoding is explicitly not MAY be used. The syntax of such an encoding is explicitly not
specified here and left to profiles or applications, specifically specified here and left to profiles or applications, specifically
note that a binary encoded scope does not necessarily use the space note that a binary encoded scope does not necessarily use the space
character '0x20' to delimit scope-tokens. character '0x20' to delimit scope-tokens.
If the AS needs to convey a hint to the RS about which profile it If the AS needs to convey a hint to the RS about which profile it
should use to communicate with the client, the AS MAY include an should use to communicate with the client, the AS MAY include an
"ace_profile" claim in the access token, with the same syntax and "ace_profile" claim in the access token, with the same syntax and
semantics as defined in Section 5.8.4.3. semantics as defined in Section 5.8.4.3.
If the client submitted a client-nonce parameter in the access token If the client submitted a client-nonce parameter in the access token
request Section 5.8.4.4, the AS MUST include the value of this request (Section 5.8.4.4), the AS MUST include the value of this
parameter in the "cnonce" claim specified here. The "cnonce" claim parameter in the "cnonce" claim specified here. The "cnonce" claim
uses binary encoding. uses binary encoding.
5.10.1. The Authorization Information Endpoint 5.10.1. The Authorization Information Endpoint
The access token, containing authorization information and The access token, containing authorization information and
information about the proof-of-possession method used by the client, information about the proof-of-possession method used by the client,
needs to be transported to the RS so that the RS can authenticate and needs to be transported to the RS so that the RS can authenticate and
authorize the client request. authorize the client request.
This section defines a method for transporting the access token to This section defines a method for transporting the access token to
the RS using a RESTful protocol such as CoAP. Profiles of this the RS using a RESTful protocol, such as CoAP. Profiles of this
framework MAY define other methods for token transport. framework MAY define other methods for token transport.
The method consists of an authz-info endpoint, implemented by the RS. The method consists of an authz-info endpoint, implemented by the RS.
A client using this method MUST make a POST request to the authz-info A client using this method MUST make a POST request to the authz-info
endpoint at the RS with the access token in the payload. The CoAP endpoint at the RS with the access token in the payload. The CoAP
Content-Format or HTTP Media Type MUST reflect the format of the Content-Format or HTTP media type MUST reflect the format of the
token, e.g. application/cwt for CBOR Web Tokens, if no Content-Format token, e.g., "application/cwt", for CBOR Web Tokens; if no Content-
or Media Type is defined for the token format, application/octet- Format or media type is defined for the token format, "application/
stream MUST be used. octet-stream" MUST be used.
The RS receiving the token MUST verify the validity of the token. If The RS receiving the token MUST verify the validity of the token. If
the token is valid, the RS MUST respond to the POST request with a the token is valid, the RS MUST respond to the POST request with a
response code equivalent to CoAP's 2.01 (Created). Section 5.10.1.1 response code equivalent to CoAP code 2.01 (Created).
outlines how an RS MUST proceed to verify the validity of an access Section 5.10.1.1 outlines how an RS MUST proceed to verify the
token. validity of an access token.
The RS MUST be prepared to store at least one access token for future The RS MUST be prepared to store at least one access token for future
use. This is a difference to how access tokens are handled in OAuth use. This is a difference as to how access tokens are handled in
2.0, where the access token is typically sent along with each OAuth 2.0, where the access token is typically sent along with each
request, and therefore not stored at the RS. request and therefore not stored at the RS.
When using this framework it is RECOMMENDED that an RS stores only When using this framework, it is RECOMMENDED that an RS stores only
one token per proof-of-possession key. This means that an additional one token per proof-of-possession key. This means that an additional
token linked to the same key will supersede any existing token at the token linked to the same key will supersede any existing token at the
RS, by replacing the corresponding authorization information. The RS by replacing the corresponding authorization information. The
reason is that this greatly simplifies (constrained) implementations, reason is that this greatly simplifies (constrained) implementations,
with respect to required storage and resolving a request to the with respect to required storage and resolving a request to the
applicable token. The use of multiple access tokens for a single applicable token. The use of multiple access tokens for a single
client increases the strain on the resource server as it must client increases the strain on the resource server, as it must
consider every access token and calculate the actual permissions of consider every access token and calculate the actual permissions of
the client. Also, tokens may contradict each other which may lead the client. Also, tokens may contradict each other, which may lead
the server to enforce wrong permissions. If one of the access tokens the server to enforce wrong permissions. If one of the access tokens
expires earlier than others, the resulting permissions may offer expires earlier than others, the resulting permissions may offer
insufficient protection. insufficient protection.
If the payload sent to the authz-info endpoint does not parse to a If the payload sent to the authz-info endpoint does not parse to a
token, the RS MUST respond with a response code equivalent to the token, the RS MUST respond with a response code equivalent to the
CoAP code 4.00 (Bad Request). CoAP code 4.00 (Bad Request).
The RS MAY make an introspection request to validate the token before The RS MAY make an introspection request to validate the token before
responding to the POST request to the authz-info endpoint, e.g. if responding to the POST request to the authz-info endpoint, e.g., if
the token is an opaque reference. Some transport protocols may the token is an opaque reference. Some transport protocols may
provide a way to indicate that the RS is busy and the client should provide a way to indicate that the RS is busy and the client should
retry after an interval; this type of status update would be retry after an interval; this type of status update would be
appropriate while the RS is waiting for an introspection response. appropriate while the RS is waiting for an introspection response.
Profiles MUST specify whether the authz-info endpoint is protected, Profiles MUST specify whether the authz-info endpoint is protected,
including whether error responses from this endpoint are protected. including whether error responses from this endpoint are protected.
Note that since the token contains information that allow the client Note that since the token contains information that allows the client
and the RS to establish a security context in the first place, mutual and the RS to establish a security context in the first place, mutual
authentication may not be possible at this point. authentication may not be possible at this point.
The default name of this endpoint in an url-path is '/authz-info', The default name of this endpoint in a url-path is '/authz-info';
however implementations are not required to use this name and can however, implementations are not required to use this name and can
define their own instead. define their own instead.
5.10.1.1. Verifying an Access Token 5.10.1.1. Verifying an Access Token
When an RS receives an access token, it MUST verify it before storing When an RS receives an access token, it MUST verify it before storing
it. The details of token verification depends on various aspects, it. The details of token verification depends on various aspects,
including the token encoding, the type of token, the security including the token encoding, the type of token, the security
protection applied to the token, and the claims. The token encoding protection applied to the token, and the claims. The token encoding
matters since the security protection differs between the token matters since the security protection differs between the token
encodings. For example, a CWT token uses COSE while a JWT token uses encodings. For example, a CWT token uses COSE, while a JWT token
JOSE. The type of token also has an influence on the verification uses JSON Object Signing and Encryption (JOSE). The type of token
procedure since tokens may be self-contained whereby token also has an influence on the verification procedure since tokens may
verification may happen locally at the RS while a token-by-reference be self-contained, whereby token verification may happen locally at
requires further interaction with the authorization server, for the RS, while a token-by-reference requires further interaction with
example using token introspection, to obtain the claims associated the authorization server, for example, using token introspection, to
with the token reference. Self-contained tokens MUST, at least be obtain the claims associated with the token reference. Self-
integrity protected but they MAY also be encrypted. contained tokens MUST at least be integrity protected, but they MAY
also be encrypted.
For self-contained tokens the RS MUST process the security protection For self-contained tokens, the RS MUST process the security
of the token first, as specified by the respective token format. For protection of the token first, as specified by the respective token
CWT the description can be found in [RFC8392] and for JWT the format. For CWT, the description can be found in [RFC8392]; for JWT,
relevant specification is [RFC7519]. This MUST include a the relevant specification is [RFC7519]. This MUST include a
verification that security protection (and thus the token) was verification that security protection (and thus the token) was
generated by an AS that has the right to issue access tokens for this generated by an AS that has the right to issue access tokens for this
RS. RS.
In case the token is communicated by reference the RS needs to obtain In case the token is communicated by reference, the RS needs to
the claims first. When the RS uses token introspection the relevant obtain the claims first. When the RS uses token introspection, the
specification is [RFC7662] with CoAP transport specified in relevant specification is [RFC7662] with CoAP transport specified in
Section 5.9. Section 5.9.
Errors may happen during this initial processing stage: Errors may happen during this initial processing stage:
* If the verification of the security wrapper fails, or the token * If the verification of the security wrapper fails, or the token
was issued by an AS that does not have the right to issue tokens was issued by an AS that does not have the right to issue tokens
for the receiving RS, the RS MUST discard the token and, if this for the receiving RS, the RS MUST discard the token and, if this
was an interaction with authz-info, return an error message with a was an interaction with authz-info, return an error message with a
response code equivalent to the CoAP code 4.01 (Unauthorized). response code equivalent to the CoAP code 4.01 (Unauthorized).
* If the claims cannot be obtained the RS MUST discard the token * If the claims cannot be obtained, the RS MUST discard the token
and, in case of an interaction via the authz-info endpoint, return and, in case of an interaction via the authz-info endpoint, return
an error message with a response code equivalent to the CoAP code an error message with a response code equivalent to the CoAP code
4.00 (Bad Request). 4.00 (Bad Request).
Next, the RS MUST verify claims, if present, contained in the access Next, the RS MUST verify claims, if present, contained in the access
token. Errors are returned when claim checks fail, in the order of token. Errors are returned when claim checks fail, in the order of
priority of this list: priority of this list:
iss The issuer claim (if present) must identify the AS that has iss
The issuer claim (if present) must identify the AS that has
produced the security protection for the access token. If that is produced the security protection for the access token. If that is
not the case the RS MUST discard the token. If this was an not the case, the RS MUST discard the token. If this was an
interaction with authz-info, the RS MUST also respond with a interaction with authz-info, the RS MUST also respond with a
response code equivalent to the CoAP code 4.01 (Unauthorized). response code equivalent to the CoAP code 4.01 (Unauthorized).
exp The expiration date must be in the future. If that is not the exp
case the RS MUST discard the token. If this was an interaction The expiration date must be in the future. If that is not the
with authz-info the RS MUST also respond with a response code case, the RS MUST discard the token. If this was an interaction
with authz-info, the RS MUST also respond with a response code
equivalent to the CoAP code 4.01 (Unauthorized). Note that the RS equivalent to the CoAP code 4.01 (Unauthorized). Note that the RS
has to terminate access rights to the protected resources at the has to terminate access rights to the protected resources at the
time when the tokens expire. time when the tokens expire.
aud The audience claim must refer to an audience that the RS aud
identifies with. If that is not the case the RS MUST discard the The audience claim must refer to an audience that the RS
identifies with. If that is not the case, the RS MUST discard the
token. If this was an interaction with authz-info, the RS MUST token. If this was an interaction with authz-info, the RS MUST
also respond with a response code equivalent to the CoAP code 4.03 also respond with a response code equivalent to the CoAP code 4.03
(Forbidden). (Forbidden).
scope The RS must recognize value of the scope claim. If that is scope
not the case the RS MUST discard the token. If this was an The RS must recognize value of the scope claim. If that is not
the case, the RS MUST discard the token. If this was an
interaction with authz-info, the RS MUST also respond with a interaction with authz-info, the RS MUST also respond with a
response code equivalent to the CoAP code 4.00 (Bad Request). The response code equivalent to the CoAP code 4.00 (Bad Request). The
RS MAY provide additional information in the error response, to RS MAY provide additional information in the error response to
clarify what went wrong. clarify what went wrong.
Additional processing may be needed for other claims in a way Additional processing may be needed for other claims in a way
specific to a profile or the underlying application. specific to a profile or the underlying application.
Note that the Subject (sub) claim cannot always be verified when the Note that the Subject (sub) claim cannot always be verified when the
token is submitted to the RS since the client may not have token is submitted to the RS since the client may not have
authenticated yet. Also note that a counter for the expires_in (exi) authenticated yet. Also note that a counter for the expires_in (exi)
claim MUST be initialized when the RS first verifies this token. claim MUST be initialized when the RS first verifies this token.
Also note that profiles of this framework may define access token Also note that profiles of this framework may define access token
transport mechanisms that do not allow for error responses. transport mechanisms that do not allow for error responses.
Therefore the error messages specified here only apply if the token Therefore, the error messages specified here only apply if the token
was sent to the authz-info endpoint. was sent to the authz-info endpoint.
When sending error responses, the RS MAY use the error codes from When sending error responses, the RS MAY use the error codes from
Section 3.1 of [RFC6750], to provide additional details to the Section 3.1 of [RFC6750] to provide additional details to the client.
client.
5.10.1.2. Protecting the Authorization Information Endpoint 5.10.1.2. Protecting the Authorization Information Endpoint
As this framework can be used in RESTful environments, it is As this framework can be used in RESTful environments, it is
important to make sure that attackers cannot perform unauthorized important to make sure that attackers cannot perform unauthorized
requests on the authz-info endpoints, other than submitting access requests on the authz-info endpoints, other than submitting access
tokens. tokens.
Specifically it SHOULD NOT be possible to perform GET, DELETE or PUT Specifically, it SHOULD NOT be possible to perform GET, DELETE, or
on the authz-info endpoint. PUT on the authz-info endpoint.
The RS SHOULD implement rate limiting measures to mitigate attacks The RS SHOULD implement rate-limiting measures to mitigate attacks
aiming to overload the processing capacity of the RS by repeatedly aiming to overload the processing capacity of the RS by repeatedly
submitting tokens. For CoAP-based communication the RS could use the submitting tokens. For CoAP-based communication, the RS could use
mechanisms from [RFC8516] to indicate that it is overloaded. the mechanisms from [RFC8516] to indicate that it is overloaded.
5.10.2. Client Requests to the RS 5.10.2. Client Requests to the RS
Before sending a request to an RS, the client MUST verify that the Before sending a request to an RS, the client MUST verify that the
keys used to protect this communication are still valid. See keys used to protect this communication are still valid. See
Section 5.10.4 for details on how the client determines the validity Section 5.10.4 for details on how the client determines the validity
of the keys used. of the keys used.
If an RS receives a request from a client, and the target resource If an RS receives a request from a client and the target resource
requires authorization, the RS MUST first verify that it has an requires authorization, the RS MUST first verify that it has an
access token that authorizes this request, and that the client has access token that authorizes this request and that the client has
performed the proof-of-possession binding that token to the request. performed the proof-of-possession binding for that token to the
request.
The response code MUST be 4.01 (Unauthorized) in case the client has The response code MUST be 4.01 (Unauthorized) in case the client has
not performed the proof-of-possession, or if RS has no valid access not performed the proof of possession or if the RS has no valid
token for the client. If RS has an access token for the client but access token for the client. If the RS has an access token for the
the token does not authorize access for the resource that was client but the token does not authorize access for the resource that
requested, RS MUST reject the request with a 4.03 (Forbidden). If RS was requested, the RS MUST reject the request with a 4.03
has an access token for the client but it does not cover the action (Forbidden). If the RS has an access token for the client but it
that was requested on the resource, RS MUST reject the request with a does not cover the action that was requested on the resource, the RS
4.05 (Method Not Allowed). MUST reject the request with a 4.05 (Method Not Allowed).
Note: The use of the response codes 4.03 and 4.05 is intended to Note: The use of the response codes 4.03 and 4.05 is intended to
prevent infinite loops where a dumb client optimistically tries to prevent infinite loops where a dumb client optimistically tries to
access a requested resource with any access token received from AS. access a requested resource with any access token received from AS.
As malicious clients could pretend to be C to determine C's As malicious clients could pretend to be the C to determine the C's
privileges, these detailed response codes must be used only when a privileges, these detailed response codes must be used only when a
certain level of security is already available which can be achieved certain level of security is already available, which can be achieved
only when the client is authenticated. only when the client is authenticated.
Note: The RS MAY use introspection for timely validation of an access Note: The RS MAY use introspection for timely validation of an access
token, at the time when a request is presented. token at the time when a request is presented.
Note: Matching the claims of the access token (e.g., scope) to a Note: Matching the claims of the access token (e.g., scope) to a
specific request is application specific. specific request is application specific.
If the request matches a valid token and the client has performed the If the request matches a valid token and the client has performed the
proof-of-possession for that token, the RS continues to process the proof of possession for that token, the RS continues to process the
request as specified by the underlying application. request as specified by the underlying application.
5.10.3. Token Expiration 5.10.3. Token Expiration
Depending on the capabilities of the RS, there are various ways in Depending on the capabilities of the RS, there are various ways in
which it can verify the expiration of a received access token. Here which it can verify the expiration of a received access token. The
follows a list of the possibilities including what functionality they following is a list of the possibilities including what functionality
require of the RS. they require of the RS.
* The token is a CWT and includes an "exp" claim and possibly the * The token is a CWT and includes an "exp" claim and possibly the
"nbf" claim. The RS verifies these by comparing them to values "nbf" claim. The RS verifies these by comparing them to values
from its internal clock as defined in [RFC7519]. In this case the from its internal clock, as defined in [RFC7519]. In this case,
RS's internal clock must reflect the current date and time, or at the RS's internal clock must reflect the current date and time or
least be synchronized with the AS's clock. How this clock at least be synchronized with the AS's clock. How this clock
synchronization would be performed is out of scope for this synchronization would be performed is out of scope for this
specification. specification.
* The RS verifies the validity of the token by performing an * The RS verifies the validity of the token by performing an
introspection request as specified in Section 5.9. This requires introspection request, as specified in Section 5.9. This requires
the RS to have a reliable network connection to the AS and to be the RS to have a reliable network connection to the AS and to be
able to handle two secure sessions in parallel (C to RS and RS to able to handle two secure sessions in parallel (C to RS and RS to
AS). AS).
* In order to support token expiration for devices that have no * In order to support token expiration for devices that have no
reliable way of synchronizing their internal clocks, this reliable way of synchronizing their internal clocks, this
specification defines the following approach: The claim "exi" specification defines the following approach: The claim "exi"
("expires in") can be used, to provide the RS with the lifetime of ("expires in") can be used to provide the RS with the lifetime of
the token in seconds from the time the RS first receives the the token in seconds from the time the RS first receives the
token. This mechanism only works for self-contained tokens, i.e. token. This mechanism only works for self-contained tokens, i.e.,
CWTs and JWTs. For CWTs this parameter is encoded as unsigned CWTs and JWTs. For CWTs, this parameter is encoded as an unsigned
integer, while JWTs encode this as JSON number. integer, while JWTs encode this as JSON number.
* Processing this claim requires that the RS does the following: * Processing this claim requires that the RS does the following:
- For each token the RS receives, that contains an "exi" claim: - For each token the RS receives that contains an "exi" claim,
Keep track of the time it received that token and revisit that keep track of the time it received that token and revisit that
list regularly to expunge expired tokens. list regularly to expunge expired tokens.
- Keep track of the identifiers of tokens containing the "exi" - Keep track of the identifiers of tokens containing the "exi"
claim that have expired (in order to avoid accepting them claim that have expired (in order to avoid accepting them
again). In order to avoid an unbounded memory usage growth, again). In order to avoid an unbounded memory usage growth,
this MUST be implemented in the following way when the "exi" this MUST be implemented in the following way when the "exi"
claim is used: claim is used:
o When creating the token, the AS MUST add a 'cti' claim ( or o When creating the token, the AS MUST add a 'cti' claim ( or
'jti' for JWTs) to the access token. The value of this 'jti' for JWTs) to the access token. The value of this
claim MUST be created as the binary representation of the claim MUST be created as the binary representation of the
concatenation of the identifier of the RS with a sequence concatenation of the identifier of the RS with a sequence
number counting the tokens containing an 'exi' claim, issued number counting the tokens containing an 'exi' claim, issued
by this AS for the RS. by this AS for the RS.
o The RS MUST store the highest sequence number of an expired o The RS MUST store the highest sequence number of an expired
token containing the "exi" claim that it has seen, and treat token containing the "exi" claim that it has seen and treat
tokens with lower sequence numbers as expired. Note that tokens with lower sequence numbers as expired. Note that
this could lead to discarding valid tokens with lower this could lead to discarding valid tokens with lower
sequence numbers, if the AS where to issue tokens of sequence numbers if the AS where to issue tokens of
different validity time for the same RS. The assumption is different validity time for the same RS. The assumption is
that typically tokens in such a scenario would all have the that typically tokens in such a scenario would all have the
same validity time. same validity time.
If a token that authorizes a long running request such as a CoAP If a token that authorizes a long-running request, such as a CoAP
Observe [RFC7641] expires, the RS MUST send an error response with Observe [RFC7641], expires, the RS MUST send an error response with
the response code equivalent to the CoAP code 4.01 (Unauthorized) to the response code equivalent to the CoAP code 4.01 (Unauthorized) to
the client and then terminate processing the long running request. the client and then terminate processing the long-running request.
5.10.4. Key Expiration 5.10.4. Key Expiration
The AS provides the client with key material that the RS uses. This The AS provides the client with key material that the RS uses. This
can either be a common symmetric PoP-key, or an asymmetric key used can either be a common symmetric PoP key or an asymmetric key used by
by the RS to authenticate towards the client. Since there is the RS to authenticate towards the client. Since there is currently
currently no expiration metadata associated to those keys, the client no expiration metadata associated to those keys, the client has no
has no way of knowing if these keys are still valid. This may lead way of knowing if these keys are still valid. This may lead to
to situations where the client sends requests containing sensitive situations where the client sends requests containing sensitive
information to the RS using a key that is expired and possibly in the information to the RS using a key that is expired and possibly in the
hands of an attacker, or accepts responses from the RS that are not hands of an attacker or where the client accepts responses from the
properly protected and could possibly have been forged by an RS that are not properly protected and could possibly have been
attacker. forged by an attacker.
In order to prevent this, the client must assume that those keys are In order to prevent this, the client must assume that those keys are
only valid as long as the related access token is. Since the access only valid as long as the related access token is. Since the access
token is opaque to the client, one of the following methods MUST be token is opaque to the client, one of the following methods MUST be
used to inform the client about the validity of an access token: used to inform the client about the validity of an access token:
* The client knows a default validity time for all tokens it is * The client knows a default validity time for all tokens it is
using (i.e. how long a token is valid after being issued). This using (i.e., how long a token is valid after being issued). This
information could be provisioned to the client when it is information could be provisioned to the client when it is
registered at the AS, or published by the AS in a way that the registered at the AS or published by the AS in a way that the
client can query. client can query.
* The AS informs the client about the token validity using the * The AS informs the client about the token validity using the
"expires_in" parameter in the Access Information. "expires_in" parameter in the Access Information.
A client that is not able to obtain information about the expiration A client that is not able to obtain information about the expiration
of a token MUST NOT use this token. of a token MUST NOT use this token.
6. Security Considerations 6. Security Considerations
Security considerations applicable to authentication and Security considerations applicable to authentication and
authorization in RESTful environments provided in OAuth 2.0 [RFC6749] authorization in RESTful environments provided in OAuth 2.0 [RFC6749]
apply to this work. Furthermore [RFC6819] provides additional apply to this work. Furthermore, [RFC6819] provides additional
security considerations for OAuth which apply to IoT deployments as security considerations for OAuth, which apply to IoT deployments as
well. If the introspection endpoint is used, the security well. If the introspection endpoint is used, the security
considerations from [RFC7662] also apply. considerations from [RFC7662] also apply.
The following subsections address issues specific to this document The following subsections address issues specific to this document
and it's use in constrained environments. and its use in constrained environments.
6.1. Protecting Tokens 6.1. Protecting Tokens
A large range of threats can be mitigated by protecting the contents A large range of threats can be mitigated by protecting the contents
of the access token by using a digital signature or a keyed message of the access token by using a digital signature or a keyed message
digest (MAC) or an Authenticated Encryption with Associated Data digest, e.g., a Message Authentication Code (MAC) or an Authenticated
(AEAD) algorithm. Consequently, the token integrity protection MUST Encryption with Associated Data (AEAD) algorithm. Consequently, the
be applied to prevent the token from being modified, particularly token integrity protection MUST be applied to prevent the token from
since it contains a reference to the symmetric key or the asymmetric being modified, particularly since it contains a reference to the
key used for proof-of-possession. If the access token contains the symmetric key or the asymmetric key used for proof of possession. If
symmetric key, this symmetric key MUST be encrypted by the the access token contains the symmetric key, this symmetric key MUST
authorization server so that only the resource server can decrypt it. be encrypted by the authorization server so that only the resource
Note that using an AEAD algorithm is preferable over using a MAC server can decrypt it. Note that using an AEAD algorithm is
unless the token needs to be publicly readable. preferable over using a MAC unless the token needs to be publicly
readable.
If the token is intended for multiple recipients (i.e. an audience If the token is intended for multiple recipients (i.e., an audience
that is a group), integrity protection of the token with a symmetric that is a group), integrity protection of the token with a symmetric
key, shared between the AS and the recipients, is not sufficient, key, shared between the AS and the recipients, is not sufficient,
since any of the recipients could modify the token undetected by the since any of the recipients could modify the token undetected by the
other recipients. Therefore a token with a multi-recipient audience other recipients. Therefore, a token with a multirecipient audience
MUST be protected with an asymmetric signature. MUST be protected with an asymmetric signature.
It is important for the authorization server to include the identity It is important for the authorization server to include the identity
of the intended recipient (the audience), typically a single resource of the intended recipient (the audience), typically a single resource
server (or a list of resource servers), in the token. The same server (or a list of resource servers), in the token. The same
shared secret MUST NOT be used as proof-of-possession key with shared secret MUST NOT be used as a proof-of-possession key with
multiple resource servers since the benefit from using the proof-of- multiple resource servers, since the benefit from using the proof-of-
possession concept is then significantly reduced. possession concept is then significantly reduced.
If clients are capable of doing so, they should frequently request If clients are capable of doing so, they should frequently request
fresh access tokens, as this allows the AS to keep the lifetime of fresh access tokens, as this allows the AS to keep the lifetime of
the tokens short. This allows the AS to use shorter proof-of- the tokens short. This allows the AS to use shorter proof-of-
possession key sizes, which translate to a performance benefit for possession key sizes, which translate to a performance benefit for
the client and for the resource server. Shorter keys also lead to the client and for the resource server. Shorter keys also lead to
shorter messages (particularly with asymmetric keying material). shorter messages (particularly with asymmetric keying material).
When authorization servers bind symmetric keys to access tokens, they When authorization servers bind symmetric keys to access tokens, they
SHOULD scope these access tokens to a specific permission. SHOULD scope these access tokens to a specific permission.
In certain situations it may be necessary to revoke an access token In certain situations, it may be necessary to revoke an access token
that is still valid. Client-initiated revocation is specified in that is still valid. Client-initiated revocation is specified in
[RFC7009] for OAuth 2.0. Other revocation mechanisms are currently [RFC7009] for OAuth 2.0. Other revocation mechanisms are currently
not specified, as the underlying assumption in OAuth is that access not specified, as the underlying assumption in OAuth is that access
tokens are issued with a relatively short lifetime. This may not tokens are issued with a relatively short lifetime. This may not
hold true for disconnected constrained devices, needing access tokens hold true for disconnected constrained devices needing access tokens
with relatively long lifetimes, and would therefore necessitate with relatively long lifetimes and would therefore necessitate
further standardization work that is out of scope for this document. further standardization work that is out of scope for this document.
6.2. Communication Security 6.2. Communication Security
Communication with the authorization server MUST use confidentiality Communication with the authorization server MUST use confidentiality
protection. This step is extremely important since the client or the protection. This step is extremely important since the client or the
RS may obtain the proof-of-possession key from the authorization RS may obtain the proof-of-possession key from the authorization
server for use with a specific access token. Not using server for use with a specific access token. Not using
confidentiality protection exposes this secret (and the access token) confidentiality protection exposes this secret (and the access token)
to an eavesdropper thereby completely negating proof-of-possession to an eavesdropper, thereby completely negating proof-of-possession
security. The requirements for communication security of profiles security. The requirements for communication security of profiles
are specified in Section 5. are specified in Section 5.
Additional protection for the access token can be applied by Additional protection for the access token can be applied by
encrypting it, for example encryption of CWTs is specified in encrypting it, for example, encryption of CWTs is specified in
Section 5.1 of [RFC8392]. Such additional protection can be Section 5.1 of [RFC8392]. Such additional protection can be
necessary if the token is later transferred over an insecure necessary if the token is later transferred over an insecure
connection (e.g. when it is sent to the authz-info endpoint). connection (e.g., when it is sent to the authz-info endpoint).
Care must by taken by developers to prevent leakage of the PoP Care must be taken by developers to prevent leakage of the PoP
credentials (i.e., the private key or the symmetric key). An credentials (i.e., the private key or the symmetric key). An
adversary in possession of the PoP credentials bound to the access adversary in possession of the PoP credentials bound to the access
token will be able to impersonate the client. Be aware that this is token will be able to impersonate the client. Be aware that this is
a real risk with many constrained environments, since adversaries may a real risk with many constrained environments, since adversaries may
get physical access to the devices and can therefore use physical get physical access to the devices and can therefore use physical
extraction techniques to gain access to memory contents. This risk extraction techniques to gain access to memory contents. This risk
can be mitigated to some extent by making sure that keys are can be mitigated to some extent by making sure that keys are
refreshed frequently, by using software isolation techniques and by refreshed frequently, by using software isolation techniques, and by
using hardware security. using hardware security.
6.3. Long-Term Credentials 6.3. Long-Term Credentials
Both clients and RSs have long-term credentials that are used to Both the clients and RSs have long-term credentials that are used to
secure communications, and authenticate to the AS. These credentials secure communications and authenticate to the AS. These credentials
need to be protected against unauthorized access. In constrained need to be protected against unauthorized access. In constrained
devices, deployed in publicly accessible places, such protection can devices deployed in publicly accessible places, such protection can
be difficult to achieve without specialized hardware (e.g. secure key be difficult to achieve without specialized hardware (e.g., secure
storage memory). key storage memory).
If credentials are lost or compromised, the operator of the affected If credentials are lost or compromised, the operator of the affected
devices needs to have procedures to invalidate any access these devices needs to have procedures to invalidate any access these
credentials give and to revoke tokens linked to such credentials. credentials give and needs to revoke tokens linked to such
The loss of a credential linked to a specific device MUST NOT lead to credentials. The loss of a credential linked to a specific device
a compromise of other credentials not linked to that device, MUST NOT lead to a compromise of other credentials not linked to that
therefore secret keys used for authentication MUST NOT be shared device; therefore, secret keys used for authentication MUST NOT be
between more than two parties. shared between more than two parties.
Operators of clients or RS SHOULD have procedures in place to replace Operators of the clients or RSs SHOULD have procedures in place to
credentials that are suspected to have been compromised or that have replace credentials that are suspected to have been compromised or
been lost. that have been lost.
Operators also SHOULD have procedures for decommissioning devices, Operators also SHOULD have procedures for decommissioning devices
that include securely erasing credentials and other security critical that include securely erasing credentials and other security-critical
material in the devices being decommissioned. material in the devices being decommissioned.
6.4. Unprotected AS Request Creation Hints 6.4. Unprotected AS Request Creation Hints
Initially, no secure channel exists to protect the communication Initially, no secure channel exists to protect the communication
between C and RS. Thus, C cannot determine if the "AS Request between the C and RS. Thus, the C cannot determine if the "AS
Creation Hints" contained in an unprotected response from RS to an Request Creation Hints" contained in an unprotected response from the
unauthorized request (see Section 5.3) are authentic. C therefore RS to an unauthorized request (see Section 5.3) are authentic.
MUST determine if an AS is authorized to provide access tokens for a Therefore, the C MUST determine if an AS is authorized to provide
certain RS. How this determination is implemented is out of scope access tokens for a certain RS. How this determination is
for this document and left to the applications. implemented is out of scope for this document and left to the
applications.
6.5. Minimal Security Requirements for Communication 6.5. Minimal Security Requirements for Communication
This section summarizes the minimal requirements for the This section summarizes the minimal requirements for the
communication security of the different protocol interactions. communication security of the different protocol interactions.
C-AS All communication between the client and the Authorization C-AS
Server MUST be encrypted, integrity and replay protected. All communication between the client and the authorization server
Furthermore responses from the AS to the client MUST be bound to MUST be encrypted and integrity and replay protected.
Furthermore, responses from the AS to the client MUST be bound to
the client's request to avoid attacks where the attacker swaps the the client's request to avoid attacks where the attacker swaps the
intended response for an older one valid for a previous request. intended response for an older one valid for a previous request.
This requires that the client and the Authorization Server have This requires that the client and the authorization server have
previously exchanged either a shared secret or their public keys previously exchanged either a shared secret or their public keys
in order to negotiate a secure communication. Furthermore the in order to negotiate a secure communication. Furthermore, the
client MUST be able to determine whether an AS has the authority client MUST be able to determine whether an AS has the authority
to issue access tokens for a certain RS. This can for example be to issue access tokens for a certain RS. This can, for example,
done through pre-configured lists, or through an online lookup be done through preconfigured lists or through an online lookup
mechanism that in turn also must be secured. mechanism that in turn also must be secured.
RS-AS The communication between the Resource Server and the RS-AS
Authorization Server via the introspection endpoint MUST be The communication between the resource server and the
encrypted, integrity and replay protected. Furthermore responses authorization server via the introspection endpoint MUST be
from the AS to the RS MUST be bound to the RS's request. This encrypted and integrity and replay protected. Furthermore,
requires that the RS and the Authorization Server have previously responses from the AS to the RS MUST be bound to the RS's request.
exchanged either a shared secret, or their public keys in order to This requires that the RS and the authorization server have
negotiate a secure communication. Furthermore the RS MUST be able previously exchanged either a shared secret or their public keys
to determine whether an AS has the authority to issue access in order to negotiate a secure communication. Furthermore, the RS
tokens itself. This is usually configured out of band, but could MUST be able to determine whether an AS has the authority to issue
also be performed through an online lookup mechanism provided that access tokens itself. This is usually configured out of band but
it is also secured in the same way. could also be performed through an online lookup mechanism,
provided that it is also secured in the same way.
C-RS The initial communication between the client and the Resource C-RS
Server can not be secured in general, since the RS is not in The initial communication between the client and the resource
server cannot be secured in general, since the RS is not in
possession of on access token for that client, which would carry possession of on access token for that client, which would carry
the necessary parameters. If both parties support DTLS without the necessary parameters. If both parties support DTLS without
client authentication it is RECOMMEND to use this mechanism for client authentication, it is RECOMMENDED to use this mechanism for
protecting the initial communication. After the client has protecting the initial communication. After the client has
successfully transmitted the access token to the RS, a secure successfully transmitted the access token to the RS, a secure
communication protocol MUST be established between client and RS communication protocol MUST be established between the client and
for the actual resource request. This protocol MUST provide RS for the actual resource request. This protocol MUST provide
confidentiality, integrity and replay protection as well as a confidentiality, integrity, and replay protection, as well as a
binding between requests and responses. This requires that the binding between requests and responses. This requires that the
client learned either the RS's public key or received a symmetric client learned either the RS's public key or received a symmetric
proof-of-possession key bound to the access token from the AS. proof-of-possession key bound to the access token from the AS.
The RS must have learned either the client's public key or a The RS must have learned either the client's public key, a shared
shared symmetric key from the claims in the token or an symmetric key from the claims in the token, or an introspection
introspection request. Since ACE does not provide profile request. Since ACE does not provide profile negotiation between
negotiation between C and RS, the client MUST have learned what the C and RS, the client MUST have learned what profile the RS
profile the RS supports (e.g. from the AS or pre-configured) and supports (e.g., from the AS or preconfigured) and initiated the
initiate the communication accordingly. communication accordingly.
6.6. Token Freshness and Expiration 6.6. Token Freshness and Expiration
An RS that is offline faces the problem of clock drift. Since it An RS that is offline faces the problem of clock drift. Since it
cannot synchronize its clock with the AS, it may be tricked into cannot synchronize its clock with the AS, it may be tricked into
accepting old access tokens that are no longer valid or have been accepting old access tokens that are no longer valid or have been
compromised. In order to prevent this, an RS may use the nonce-based compromised. In order to prevent this, an RS may use the nonce-based
mechanism (cnonce) defined in Section 5.3 to ensure freshness of an mechanism (cnonce) defined in Section 5.3 to ensure freshness of an
Access Token subsequently presented to this RS. Access Token subsequently presented to this RS.
Another problem with clock drift is that evaluating the standard Another problem with clock drift is that evaluating the standard
token expiration claim "exp" can give unpredictable results. token expiration claim "exp" can give unpredictable results.
Acceptable ranges of clock drift are highly dependent on the concrete Acceptable ranges of clock drift are highly dependent on the concrete
application. Important factors are how long access tokens are valid, application. Important factors are how long access tokens are valid
and how critical timely expiration of access token is. and how critical timely expiration of the access token is.
The expiration mechanism implemented by the "exi" claim, based on the The expiration mechanism implemented by the "exi" claim, based on the
first time the RS sees the token was defined to provide a more first time the RS sees the token, was defined to provide a more
predictable alternative. The "exi" approach has some drawbacks that predictable alternative. The "exi" approach has some drawbacks that
need to be considered: need to be considered:
A malicious client may hold back tokens with the "exi" claim in * A malicious client may hold back tokens with the "exi" claim in
order to prolong their lifespan. order to prolong their lifespan.
If an RS loses state (e.g. due to an unscheduled reboot), it may * If an RS loses state (e.g., due to an unscheduled reboot), it may
lose the current values of counters tracking the "exi" claims of lose the current values of counters tracking the "exi" claims of
tokens it is storing. tokens it is storing.
The first drawback is inherent to the deployment scenario and the The first drawback is inherent to the deployment scenario and the
"exi" solution. It can therefore not be mitigated without requiring "exi" solution. It can therefore not be mitigated without requiring
the RS be online at times. The second drawback can be mitigated by the RS be online at times. The second drawback can be mitigated by
regularly storing the value of "exi" counters to persistent memory. regularly storing the value of "exi" counters to persistent memory.
6.7. Combining Profiles 6.7. Combining Profiles
There may be use cases where different transport and security There may be use cases where different transport and security
protocols are allowed for the different interactions, and, if that is protocols are allowed for the different interactions, and, if that is
not explicitly covered by an existing profile, it corresponds to not explicitly covered by an existing profile, it corresponds to
combining profiles into a new one. For example, a new profile could combining profiles into a new one. For example, a new profile could
specify that a previously-defined MQTT-TLS profile is used between specify that a previously defined MQTT-TLS profile is used between
the client and the RS in combination with a previously-defined CoAP- the client and the RS in combination with a previously defined CoAP-
DTLS profile for interactions between the client and the AS. The new DTLS profile for interactions between the client and the AS. The new
profile that combines existing profiles MUST specify how the existing profile that combines existing profiles MUST specify how the existing
profiles' security properties are achieved. Any profile therefore profiles' security properties are achieved. Therefore, any profile
MUST clearly specify its security requirements and MUST document if MUST clearly specify its security requirements and MUST document if
its security depends on the combination of various protocol its security depends on the combination of various protocol
interactions. interactions.
6.8. Unprotected Information 6.8. Unprotected Information
Communication with the authz-info endpoint, as well as the various Communication with the authz-info endpoint, as well as the various
error responses defined in this framework, all potentially include error responses defined in this framework, potentially includes
sending information over an unprotected channel. These messages may sending information over an unprotected channel. These messages may
leak information to an adversary, or may be manipulated by active leak information to an adversary or may be manipulated by active
attackers to induce incorrect behavior. For example error responses attackers to induce incorrect behavior. For example, error responses
for requests to the Authorization Information endpoint can reveal for requests to the authorization information endpoint can reveal
information about an otherwise opaque access token to an adversary information about an otherwise opaque access token to an adversary
who has intercepted this token. who has intercepted this token.
As far as error messages are concerned, this framework is written As far as error messages are concerned, this framework is written
under the assumption that, in general, the benefits of detailed error under the assumption that, in general, the benefits of detailed error
messages outweigh the risk due to information leakage. For messages outweigh the risk due to information leakage. For
particular use cases, where this assessment does not apply, detailed particular use cases where this assessment does not apply, detailed
error messages can be replaced by more generic ones. error messages can be replaced by more generic ones.
In some scenarios it may be possible to protect the communication In some scenarios, it may be possible to protect the communication
with the authz-info endpoint (e.g. through DTLS with only server-side with the authz-info endpoint (e.g., through DTLS with only server-
authentication). In cases where this is not possible, it is side authentication). In cases where this is not possible, it is
RECOMMENDED to use encrypted CWTs or tokens that are opaque RECOMMENDED to use encrypted CWTs or tokens that are opaque
references and need to be subjected to introspection by the RS. references and need to be subjected to introspection by the RS.
If the initial unauthorized resource request message (see If the initial Unauthorized Resource Request message (see
Section 5.2) is used, the client MUST make sure that it is not Section 5.2) is used, the client MUST make sure that it is not
sending sensitive content in this request. While GET and DELETE sending sensitive content in this request. While GET and DELETE
requests only reveal the target URI of the resource, POST and PUT requests only reveal the target URI of the resource, POST and PUT
requests would reveal the whole payload of the intended operation. requests would reveal the whole payload of the intended operation.
Since the client is not authenticated at the point when it is Since the client is not authenticated at the point when it is
submitting an access token to the authz-info endpoint, attackers may submitting an access token to the authz-info endpoint, attackers may
be pretending to be a client and trying to trick an RS to use an be pretending to be a client and trying to trick an RS to use an
obsolete profile that in turn specifies a vulnerable security obsolete profile that in turn specifies a vulnerable security
mechanism via the authz-info endpoint. Such an attack would require mechanism via the authz-info endpoint. Such an attack would require
a valid access token containing an "ace_profile" claim requesting the a valid access token containing an "ace_profile" claim requesting the
use of said obsolete profile. Resource Owners should update the use of said obsolete profile. Resource owners should update the
configuration of their RS's to prevent them from using such obsolete configuration of their RSs to prevent them from using such obsolete
profiles. profiles.
6.9. Identifying Audiences 6.9. Identifying Audiences
The audience claim as defined in [RFC7519] and the equivalent The audience claim, as defined in [RFC7519], and the equivalent
"audience" parameter from [RFC8693] are intentionally vague on how to "audience" parameter from [RFC8693] are intentionally vague on how to
match the audience value to a specific RS. This is intended to allow match the audience value to a specific RS. This is intended to allow
application specific semantics to be used. This section attempts to application-specific semantics to be used. This section attempts to
give some general guidance for the use of audiences in constrained give some general guidance for the use of audiences in constrained
environments. environments.
URLs are not a good way of identifying mobile devices that can switch URLs are not a good way of identifying mobile devices that can switch
networks and thus be associated with new URLs. If the audience networks and thus be associated with new URLs. If the audience
represents a single RS, and asymmetric keys are used, the RS can be represents a single RS and asymmetric keys are used, the RS can be
uniquely identified by a hash of its public key. If this approach is uniquely identified by a hash of its public key. If this approach is
used it is RECOMMENDED to apply the procedure from section 3 of used, it is RECOMMENDED to apply the procedure from Section 3 of
[RFC6920]. [RFC6920].
If the audience addresses a group of resource servers, the mapping of If the audience addresses a group of resource servers, the mapping of
group identifier to individual RS has to be provisioned to each RS a group identifier to an individual RS has to be provisioned to each
before the group-audience is usable. Managing dynamic groups could RS before the group-audience is usable. Managing dynamic groups
be an issue, if any RS is not always reachable when the groups' could be an issue if any RS is not always reachable when the groups'
memberships change. Furthermore, issuing access tokens bound to memberships change. Furthermore, issuing access tokens bound to
symmetric proof-of-possession keys that apply to a group-audience is symmetric proof-of-possession keys that apply to a group-audience is
problematic, as an RS that is in possession of the access token can problematic, as an RS that is in possession of the access token can
impersonate the client towards the other RSs that are part of the impersonate the client towards the other RSs that are part of the
group. It is therefore NOT RECOMMENDED to issue access tokens bound group. It is therefore NOT RECOMMENDED to issue access tokens bound
to a group audience and symmetric proof-of possession keys. to a group audience and symmetric proof-of possession keys.
Even the client must be able to determine the correct values to put Even the client must be able to determine the correct values to put
into the "audience" parameter, in order to obtain a token for the into the "audience" parameter in order to obtain a token for the
intended RS. Errors in this process can lead to the client intended RS. Errors in this process can lead to the client
inadvertently obtaining a token for the wrong RS. The correct values inadvertently obtaining a token for the wrong RS. The correct values
for "audience" can either be provisioned to the client as part of its for "audience" can either be provisioned to the client as part of its
configuration, or dynamically looked up by the client in some configuration or dynamically looked up by the client in some
directory. In the latter case the integrity and correctness of the directory. In the latter case, the integrity and correctness of the
directory data must be assured. Note that the "audience" hint directory data must be assured. Note that the "audience" hint
provided by the RS as part of the "AS Request Creation Hints" provided by the RS as part of the "AS Request Creation Hints"
Section 5.3 is not typically source authenticated and integrity (Section 5.3) is not typically source authenticated and integrity
protected, and should therefore not be treated a trusted value. protected and should therefore not be treated a trusted value.
6.10. Denial of Service Against or with Introspection 6.10. Denial of Service Against or with Introspection
The optional introspection mechanism provided by OAuth and supported The optional introspection mechanism provided by OAuth and supported
in the ACE framework allows for two types of attacks that need to be in the ACE framework allows for two types of attacks that need to be
considered by implementers. considered by implementers.
First, an attacker could perform a denial of service attack against First, an attacker could perform a denial-of-service attack against
the introspection endpoint at the AS in order to prevent validation the introspection endpoint at the AS in order to prevent validation
of access tokens. To maintain the security of the system, an RS that of access tokens. To maintain the security of the system, an RS that
is configured to use introspection MUST NOT allow access based on a is configured to use introspection MUST NOT allow access based on a
token for which it couldn't reach the introspection endpoint. token for which it couldn't reach the introspection endpoint.
Second, an attacker could use the fact that an RS performs Second, an attacker could use the fact that an RS performs
introspection to perform a denial of service attack against that RS introspection to perform a denial-of-service attack against that RS
by repeatedly sending tokens to its authz-info endpoint that require by repeatedly sending tokens to its authz-info endpoint that require
an introspection call. RS can mitigate such attacks by implementing an introspection call. The RS can mitigate such attacks by
rate limits on how many introspection requests they perform in a implementing rate limits on how many introspection requests they
given time interval for a certain client IP address submitting tokens perform in a given time interval for a certain client IP address
to /authz-info. When that limit has been reached, incoming requests submitting tokens to /authz-info. When that limit has been reached,
from that address are rejected for a certain amount of time. A incoming requests from that address are rejected for a certain amount
general rate limit on the introspection requests should also be of time. A general rate limit on the introspection requests should
considered, to mitigate distributed attacks. also be considered in order to mitigate distributed attacks.
7. Privacy Considerations 7. Privacy Considerations
Implementers and users should be aware of the privacy implications of Implementers and users should be aware of the privacy implications of
the different possible deployments of this framework. the different possible deployments of this framework.
The AS is in a very central position and can potentially learn The AS is in a very central position and can potentially learn
sensitive information about the clients requesting access tokens. If sensitive information about the clients requesting access tokens. If
the client credentials grant is used, the AS can track what kind of the client credentials grant is used, the AS can track what kind of
access the client intends to perform. With other grants this can be access the client intends to perform. With other grants, this can be
prevented by the Resource Owner. To do so, the resource owner needs prevented by the resource owner. To do so, the resource owner needs
to bind the grants it issues to anonymous, ephemeral credentials that to bind the grants it issues to anonymous, ephemeral credentials that
do not allow the AS to link different grants and thus different do not allow the AS to link different grants and thus different
access token requests by the same client. access token requests by the same client.
The claims contained in a token can reveal privacy sensitive The claims contained in a token can reveal privacy-sensitive
information about the client and the RS to any party having access to information about the client and the RS to any party having access to
them (whether by processing the content of a self-contained token or them (whether by processing the content of a self-contained token or
by introspection). The AS SHOULD be configured to minimize the by introspection). The AS SHOULD be configured to minimize the
information about clients and RSs disclosed in the tokens it issues. information about clients and RSs disclosed in the tokens it issues.
If tokens are only integrity protected and not encrypted, they may If tokens are only integrity protected and not encrypted, they may
reveal information to attackers listening on the wire, or able to reveal information to attackers listening on the wire or be able to
acquire the access tokens in some other way. In the case of CWTs the acquire the access tokens in some other way. In the case of CWTs,
token may, e.g., reveal the audience, the scope and the confirmation the token may, e.g., reveal the audience, the scope, and the
method used by the client. The latter may reveal the identity of the confirmation method used by the client. The latter may reveal the
device or application running the client. This may be linkable to identity of the device or application running the client. This may
the identity of the person using the client (if there is a person and be linkable to the identity of the person using the client (if there
not a machine-to-machine interaction). is a person and not a machine-to-machine interaction).
Clients using asymmetric keys for proof-of-possession should be aware Clients using asymmetric keys for proof of possession should be aware
of the consequences of using the same key pair for proof-of- of the consequences of using the same key pair for proof of
possession towards different RSs. A set of colluding RSs or an possession towards different RSs. A set of colluding RSs or an
attacker able to obtain the access tokens will be able to link the attacker able to obtain the access tokens will be able to link the
requests, or even to determine the client's identity. requests or even to determine the client's identity.
An unprotected response to an unauthorized request (see Section 5.3) An unprotected response to an unauthorized request (see Section 5.3)
may disclose information about RS and/or its existing relationship may disclose information about the RS and/or its existing
with C. It is advisable to include as little information as possible relationship with the C. It is advisable to include as little
in an unencrypted response. Even the absolute URI of the AS may information as possible in an unencrypted response. Even the
reveal sensitive information about the service that RS provides. absolute URI of the AS may reveal sensitive information about the
Developers must ensure that the RS does not disclose information that service that the RS provides. Developers must ensure that the RS
has an impact on the privacy of the stakeholders in the "AS Request does not disclose information that has an impact on the privacy of
Creation Hints". They may choose to use a different mechanism for the stakeholders in the "AS Request Creation Hints". They may choose
the discovery of the AS if necessary. If means of encrypting to use a different mechanism for the discovery of the AS if
communication between C and RS already exist, more detailed necessary. If means of encrypting communication between the C and RS
information may be included with an error response to provide C with already exist, more detailed information may be included with an
sufficient information to react on that particular error. error response to provide the C with sufficient information to react
on that particular error.
8. IANA Considerations 8. IANA Considerations
This document creates several registries with a registration policy This document creates several registries with a registration policy
of "Expert Review"; guidelines to the experts are given in of Expert Review; guidelines to the experts are given in
Section 8.17. Section 8.17.
8.1. ACE Authorization Server Request Creation Hints 8.1. ACE Authorization Server Request Creation Hints
This specification establishes the IANA "ACE Authorization Server This specification establishes the IANA "ACE Authorization Server
Request Creation Hints" registry. The registry has been created to Request Creation Hints" registry.
use the "Expert Review" registration procedure [RFC8126]. It should
be noted that, in addition to the expert review, some portions of the
registry require a specification, potentially a Standards Track RFC,
be supplied as well.
The columns of the registry are: The columns of the registry are:
Name The name of the parameter Name: The name of the parameter.
CBOR Key CBOR map key for the parameter. Different ranges of values CBOR Key: CBOR map key for the parameter. Different ranges of
use different registration policies [RFC8126]. Integer values values use different registration policies [RFC8126]. Integer
from -256 to 255 are designated as Standards Action. Integer values from -256 to 255 are designated as Standards Action.
values from -65536 to -257 and from 256 to 65535 are designated as Integer values from -65536 to -257 and from 256 to 65535 are
Specification Required. Integer values greater than 65535 are designated as Specification Required. Integer values greater than
designated as Expert Review. Integer values less than -65536 are 65535 are designated as Expert Review. Integer values less than
marked as Private Use. -65536 are marked as Private Use.
Value Type The CBOR data types allowable for the values of this Value Type: The CBOR data types allowable for the values of this
parameter. parameter.
Reference This contains a pointer to the public specification of the Reference: This contains a pointer to the public specification of
request creation hint abbreviation, if one exists. the Request Creation Hint abbreviation, if one exists.
This registry will be initially populated by the values in Figure 2. This registry has been initially populated by the values in Table 1.
The Reference column for all of these entries will be this document. The Reference column for all of these entries is this document.
8.2. CoRE Resource Type Registry 8.2. CoRE Resource Type Registry
IANA is requested to register a new Resource Type (rt=) Link Target IANA has registered a new Resource Type (rt=) Link Target Attribute
Attribute in the "Resource Type (rt=) Link Target Attribute Values" in the "Resource Type (rt=) Link Target Attribute Values" subregistry
subregistry under the "Constrained RESTful Environments (CoRE) under the "Constrained RESTful Environments (CoRE) Parameters"
Parameters" [IANA.CoreParameters] registry: [IANA.CoreParameters] registry:
* Value: "ace.ai" Value: ace.ai
* Description: ACE-OAuth authz-info endpoint resource. Description: ACE-OAuth authz-info endpoint resource.
* Reference: [this document] Reference: RFC 9200
Specific ACE-OAuth profiles can use this common resource type for Specific ACE-OAuth profiles can use this common resource type for
defining their profile-specific discovery processes. defining their profile-specific discovery processes.
8.3. OAuth Extensions Error Registration 8.3. OAuth Extensions Error Registration
This specification registers the following error values in the OAuth This specification registers the following error values in the OAuth
Extensions Error registry [IANA.OAuthExtensionsErrorRegistry]. Extensions Error registry [IANA.OAuthExtensionsErrorRegistry].
* Error name: "unsupported_pop_key" Error name: unsupported_pop_key
* Error usage location: token error response Error usage location: token error response
* Related protocol extension: [this document] Related protocol extension: RFC 9200
* Change Controller: IETF Change Controller: IETF
* Specification document(s): Section 5.8.3 of [this document] Specification document(s): Section 5.8.3 of RFC 9200
* Error name: "incompatible_ace_profiles" Error name: incompatible_ace_profiles
* Error usage location: token error response Error usage location: token error response
* Related protocol extension: [this document] Related protocol extension: RFC 9200
* Change Controller: IETF Change Controller: IETF
* Specification document(s): Section 5.8.3 of [this document] Specification document(s): Section 5.8.3 of RFC 9200
8.4. OAuth Error Code CBOR Mappings Registry 8.4. OAuth Error Code CBOR Mappings Registry
This specification establishes the IANA "OAuth Error Code CBOR This specification establishes the IANA "OAuth Error Code CBOR
Mappings" registry. The registry has been created to use the "Expert Mappings" registry.
Review" registration procedure [RFC8126], except for the value range
designated for private use.
The columns of the registry are: The columns of the registry are:
Name The OAuth Error Code name, refers to the name in Section 5.2. Name: The OAuth Error Code name, refers to the name in Section 5.2
of [RFC6749], e.g., "invalid_request". of [RFC6749], e.g., "invalid_request".
CBOR Value CBOR abbreviation for this error code. Integer values
less than -65536 are marked as "Private Use", all other values use CBOR Value: CBOR abbreviation for this error code. Integer values
the registration policy "Expert Review" [RFC8126]. less than -65536 are marked as Private Use; all other values use
Reference This contains a pointer to the public specification of the the registration policy Expert Review [RFC8126].
error code abbreviation, if one exists.
Original Specification This contains a pointer to the public Reference: This contains a pointer to the public specification of
the error code abbreviation, if one exists.
Original Specification: This contains a pointer to the public
specification of the error code, if one exists. specification of the error code, if one exists.
This registry will be initially populated by the values in Figure 10. This registry has been initially populated by the values in Table 3.
The Reference column for all of these entries will be this document. The Reference column for all of these entries is this document.
8.5. OAuth Grant Type CBOR Mappings 8.5. OAuth Grant Type CBOR Mappings
This specification establishes the IANA "OAuth Grant Type CBOR This specification establishes the IANA "OAuth Grant Type CBOR
Mappings" registry. The registry has been created to use the "Expert Mappings" registry.
Review" registration procedure [RFC8126], except for the value range
designated for private use.
The columns of this registry are: The columns of this registry are:
Name The name of the grant type as specified in Section 1.3 of Name: The name of the grant type, as specified in Section 1.3 of
[RFC6749]. [RFC6749].
CBOR Value CBOR abbreviation for this grant type. Integer values
less than -65536 are marked as "Private Use", all other values use CBOR Value: CBOR abbreviation for this grant type. Integer values
the registration policy "Expert Review" [RFC8126]. less than -65536 are marked as Private Use; all other values use
Reference This contains a pointer to the public specification of the the registration policy Expert Review [RFC8126].
grant type abbreviation, if one exists.
Original Specification This contains a pointer to the public Reference: This contains a pointer to the public specification of
the grant type abbreviation, if one exists.
Original Specification: This contains a pointer to the public
specification of the grant type, if one exists. specification of the grant type, if one exists.
This registry will be initially populated by the values in Figure 11. This registry has been initially populated by the values in Table 4.
The Reference column for all of these entries will be this document. The Reference column for all of these entries is this document.
8.6. OAuth Access Token Types 8.6. OAuth Access Token Types
This section registers the following new token type in the "OAuth This section registers the following new token type in the "OAuth
Access Token Types" registry [IANA.OAuthAccessTokenTypes]. Access Token Types" registry [IANA.OAuthAccessTokenTypes].
* Type name: "PoP" Type name: PoP
* Additional Token Endpoint Response Parameters: "cnf", "rs_cnf" see Additional Token Endpoint Response Parameters: "cnf", "rs_cnf" (see
section 3.1 of [RFC8747] and section 3.1 of Section 3.1 of [RFC8747] Section 3.2 of [RFC9201]).
[I-D.ietf-ace-oauth-params]. HTTP Authentication Scheme(s): N/A
* HTTP Authentication Scheme(s): N/A Change Controller: IETF
* Change Controller: IETF Specification document(s): RFC 9200
* Specification document(s): [this document]
8.7. OAuth Access Token Type CBOR Mappings 8.7. OAuth Access Token Type CBOR Mappings
This specification established the IANA "OAuth Access Token Type CBOR This specification establishes the IANA "OAuth Access Token Type CBOR
Mappings" registry. The registry has been created to use the "Expert Mappings" registry.
Review" registration procedure [RFC8126], except for the value range
designated for private use.
The columns of this registry are: The columns of this registry are:
Name The name of token type as registered in the OAuth Access Token Name: The name of the token type, as registered in the "OAuth Access
Types registry, e.g., "Bearer". Token Types" registry, e.g., "Bearer".
CBOR Value CBOR abbreviation for this token type. Integer values
less than -65536 are marked as "Private Use", all other values use CBOR Value: CBOR abbreviation for this token type. Integer values
the registration policy "Expert Review" [RFC8126]. less than -65536 are marked as Private Use; all other values use
Reference This contains a pointer to the public specification of the the registration policy Expert Review [RFC8126].
OAuth token type abbreviation, if one exists.
Original Specification This contains a pointer to the public Reference: This contains a pointer to the public specification of
the OAuth token type abbreviation, if one exists.
Original Specification: This contains a pointer to the public
specification of the OAuth token type, if one exists. specification of the OAuth token type, if one exists.
8.7.1. Initial Registry Contents 8.7.1. Initial Registry Contents
* Name: "Bearer" Name: Bearer
* Value: 1 Value: 1
* Reference: [this document] Reference: RFC 9200
* Original Specification: [RFC6749] Original Specification: [RFC6749]
* Name: "PoP" Name: PoP
* Value: 2 Value: 2
* Reference: [this document] Reference: RFC 9200
* Original Specification: [this document] Original Specification: RFC 9200
8.8. ACE Profile Registry 8.8. ACE Profile Registry
This specification establishes the IANA "ACE Profile" registry. The This specification establishes the IANA "ACE Profile" registry.
registry has been created to use the "Expert Review" registration
procedure [RFC8126]. It should be noted that, in addition to the
expert review, some portions of the registry require a specification,
potentially a Standards Track RFC, be supplied as well.
The columns of this registry are: The columns of this registry are:
Name The name of the profile, to be used as value of the profile Name: The name of the profile to be used as the value of the profile
attribute. attribute.
Description Text giving an overview of the profile and the context
Description: Text giving an overview of the profile and the context
it is developed for. it is developed for.
CBOR Value CBOR abbreviation for this profile name. Different
CBOR Value: CBOR abbreviation for this profile name. Different
ranges of values use different registration policies [RFC8126]. ranges of values use different registration policies [RFC8126].
Integer values from -256 to 255 are designated as Standards Integer values from -256 to 255 are designated as Standards
Action. Integer values from -65536 to -257 and from 256 to 65535 Action. Integer values from -65536 to -257 and from 256 to 65535
are designated as Specification Required. Integer values greater are designated as Specification Required. Integer values greater
than 65535 are designated as "Expert Review". Integer values less than 65535 are designated as Expert Review. Integer values less
than -65536 are marked as Private Use. than -65536 are marked as Private Use.
Reference This contains a pointer to the public specification of the
profile abbreviation, if one exists.
This registry will be initially empty and will be populated by the Reference: This contains a pointer to the public specification of
registrations from the ACE framework profiles. the profile abbreviation, if one exists.
8.9. OAuth Parameter Registration 8.9. OAuth Parameter Registration
This specification registers the following parameter in the "OAuth This specification registers the following parameter in the "OAuth
Parameters" registry [IANA.OAuthParameters]: Parameters" registry [IANA.OAuthParameters]:
* Name: "ace_profile" Name: ace_profile
* Parameter Usage Location: token response Parameter Usage Location: token response
* Change Controller: IETF Change Controller: IETF
* Reference: Section 5.8.2 and Section 5.8.4.3 of [this document] Reference: Sections 5.8.2 and 5.8.4.3 of RFC 9200
8.10. OAuth Parameters CBOR Mappings Registry 8.10. OAuth Parameters CBOR Mappings Registry
This specification establishes the IANA "OAuth Parameters CBOR This specification establishes the IANA "OAuth Parameters CBOR
Mappings" registry. The registry has been created to use the "Expert Mappings" registry.
Review" registration procedure [RFC8126], except for the value range
designated for private use.
The columns of this registry are: The columns of this registry are:
Name The OAuth Parameter name, refers to the name in the OAuth Name: The OAuth Parameter name, refers to the name in the OAuth
parameter registry, e.g., "client_id". parameter registry, e.g., "client_id".
CBOR Key CBOR map key for this parameter. Integer values less than CBOR Key: CBOR map key for this parameter. Integer values less than
-65536 are marked as "Private Use", all other values use the -65536 are marked as Private Use; all other values use the
registration policy "Expert Review" [RFC8126]. registration policy Expert Review [RFC8126].
Value Type The allowable CBOR data types for values of this
Value Type: The allowable CBOR data types for values of this
parameter. parameter.
Reference This contains a pointer to the public specification of the
OAuth parameter abbreviation, if one exists. Reference: This contains a pointer to the public specification of
the OAuth parameter abbreviation, if one exists.
Original Specification This contains a pointer to the public Original Specification This contains a pointer to the public
specification of the OAuth parameter, if one exists. specification of the OAuth parameter, if one exists.
This registry will be initially populated by the values in Figure 12. This registry has been initially populated by the values in Table 5.
The Reference column for all of these entries will be this document. The Reference column for all of these entries is this document.
8.11. OAuth Introspection Response Parameter Registration 8.11. OAuth Introspection Response Parameter Registration
This specification registers the following parameters in the OAuth This specification registers the following parameters in the OAuth
Token Introspection Response registry Token Introspection Response registry
[IANA.TokenIntrospectionResponse]. [IANA.TokenIntrospectionResponse].
* Name: "ace_profile" Name: ace_profile
* Description: The ACE profile used between client and RS. Description: The ACE profile used between the client and RS.
* Change Controller: IETF Change Controller: IETF
* Reference: Section 5.9.2 of [this document] Reference: Section 5.9.2 of RFC 9200
* Name: "cnonce" Name: cnonce
* Description: "client-nonce". A nonce previously provided to the
AS by the RS via the client. Used to verify token freshness when
the RS cannot synchronize its clock with the AS.
* Change Controller: IETF
* Reference: Section 5.9.2 of [this document]
* Name: "cti" Description: "client-nonce". A nonce previously provided to the AS
* Description: "CWT ID". The identifier of a CWT as defined in by the RS via the client. Used to verify token freshness when the
RS cannot synchronize its clock with the AS.
Change Controller: IETF
Reference: Section 5.9.2 of RFC 9200
Name cti
Description "CWT ID". The identifier of a CWT as defined in
[RFC8392]. [RFC8392].
* Change Controller: IETF Change Controller IETF
* Reference: Section 5.9.2 of [this document] Reference Section 5.9.2 of RFC 9200
* Name: "exi" Name: exi
* Description: "Expires in". Lifetime of the token in seconds from Description: "Expires in". Lifetime of the token in seconds from
the time the RS first sees it. Used to implement a weaker from of the time the RS first sees it. Used to implement a weaker form of
token expiration for devices that cannot synchronize their token expiration for devices that cannot synchronize their
internal clocks. internal clocks.
* Change Controller: IETF Change Controller: IETF
* Reference: Section 5.9.2 of [this document] Reference: Section 5.9.2 of RFC 9200
8.12. OAuth Token Introspection Response CBOR Mappings Registry 8.12. OAuth Token Introspection Response CBOR Mappings Registry
This specification establishes the IANA "OAuth Token Introspection This specification establishes the IANA "OAuth Token Introspection
Response CBOR Mappings" registry. The registry has been created to Response CBOR Mappings" registry.
use the "Expert Review" registration procedure [RFC8126], except for
the value range designated for private use.
The columns of this registry are: The columns of this registry are:
Name The OAuth Parameter name, refers to the name in the OAuth Name: The OAuth Parameter name, refers to the name in the OAuth
parameter registry, e.g., "client_id". parameter registry, e.g., "client_id".
CBOR Key CBOR map key for this parameter. Integer values less than
-65536 are marked as "Private Use", all other values use the CBOR Key: CBOR map key for this parameter. Integer values less than
registration policy "Expert Review" [RFC8126]. -65536 are marked as Private Use; all other values use the
Value Type The allowable CBOR data types for values of this registration policy Expert Review [RFC8126].
Value Type: The allowable CBOR data types for values of this
parameter. parameter.
Reference This contains a pointer to the public specification of the
introspection response parameter abbreviation, if one exists. Reference: This contains a pointer to the public specification of
the introspection response parameter abbreviation, if one exists.
Original Specification This contains a pointer to the public Original Specification This contains a pointer to the public
specification of OAuth Token Introspection parameter, if one specification of the OAuth Token Introspection parameter, if one
exists. exists.
This registry will be initially populated by the values in Figure 16. This registry has been initially populated by the values in Table 6.
The Reference column for all of these entries will be this document. The Reference column for all of these entries is this document.
Note that the mappings of parameters corresponding to claim names Note that the mappings of parameters corresponding to claim names
intentionally coincide with the CWT claim name mappings from intentionally coincide with the CWT claim name mappings from
[RFC8392]. [RFC8392].
8.13. JSON Web Token Claims 8.13. JSON Web Token Claims
This specification registers the following new claims in the JSON Web This specification registers the following new claims in the JSON Web
Token (JWT) registry of JSON Web Token Claims Token (JWT) registry of JSON Web Token Claims
[IANA.JsonWebTokenClaims]: [IANA.JsonWebTokenClaims]:
* Claim Name: "ace_profile" Claim Name: ace_profile
* Claim Description: The ACE profile a token is supposed to be used Claim Description: The ACE profile a token is supposed to be used
with. with.
* Change Controller: IETF Change Controller: IETF
* Reference: Section 5.10 of [this document] Reference: Section 5.10 of RFC 9200
* Claim Name: "cnonce" Claim Name: cnonce
* Claim Description: "client-nonce". A nonce previously provided to Claim Description: "client-nonce". A nonce previously provided to
the AS by the RS via the client. Used to verify token freshness the AS by the RS via the client. Used to verify token freshness
when the RS cannot synchronize its clock with the AS. when the RS cannot synchronize its clock with the AS.
* Change Controller: IETF Change Controller: IETF
* Reference: Section 5.10 of [this document] Reference: Section 5.10 of RFC 9200
* Claim Name: "exi"
* Claim Description: "Expires in". Lifetime of the token in seconds Claim Name: exi
Claim Description: "Expires in". Lifetime of the token in seconds
from the time the RS first sees it. Used to implement a weaker from the time the RS first sees it. Used to implement a weaker
from of token expiration for devices that cannot synchronize their form of token expiration for devices that cannot synchronize their
internal clocks. internal clocks.
* Change Controller: IETF Change Controller: IETF
* Reference: Section 5.10.3 of [this document] Reference: Section 5.10.3 of RFC 9200
8.14. CBOR Web Token Claims 8.14. CBOR Web Token Claims
This specification registers the following new claims in the "CBOR This specification registers the following new claims in the "CBOR
Web Token (CWT) Claims" registry [IANA.CborWebTokenClaims]. Web Token (CWT) Claims" registry [IANA.CborWebTokenClaims].
* Claim Name: "ace_profile" Claim Name: ace_profile
* Claim Description: The ACE profile a token is supposed to be used Claim Description: The ACE profile a token is supposed to be used
with. with.
* JWT Claim Name: ace_profile JWT Claim Name: ace_profile
* Claim Key: TBD (suggested: 38) Claim Key: 38
* Claim Value Type(s): integer Claim Value Type(s): integer
* Change Controller: IETF Change Controller: IETF
* Specification Document(s): Section 5.10 of [this document] Specification Document(s): Section 5.10 of RFC 9200
* Claim Name: "cnonce" Claim Name: cnonce
* Claim Description: The client-nonce sent to the AS by the RS via Claim Description: The client-nonce sent to the AS by the RS via the
the client. client.
* JWT Claim Name: cnonce JWT Claim Name: cnonce
* Claim Key: TBD (suggested: 39) Claim Key: 39
* Claim Value Type(s): byte string Claim Value Type(s): byte string
* Change Controller: IETF Change Controller: IETF
* Specification Document(s): Section 5.10 of [this document] Specification Document(s): Section 5.10 of RFC 9200
* Claim Name: "exi" Claim Name: exi
* Claim Description: The expiration time of a token measured from Claim Description: The expiration time of a token measured from when
when it was received at the RS in seconds. it was received at the RS in seconds.
* JWT Claim Name: exi JWT Claim Name: exi
* Claim Key: TBD (suggested: 40) Claim Key: 40
* Claim Value Type(s): integer Claim Value Type(s): integer
* Change Controller: IETF Change Controller: IETF
* Specification Document(s): Section 5.10.3 of [this document] Specification Document(s): Section 5.10.3 of RFC 9200
* Claim Name: "scope" Claim Name: scope
* Claim Description: The scope of an access token as defined in Claim Description: The scope of an access token, as defined in
[RFC6749]. [RFC6749].
* JWT Claim Name: scope JWT Claim Name: scope
* Claim Key: TBD (suggested: 9) Claim Key: 9
* Claim Value Type(s): byte string or text string Claim Value Type(s): byte string or text string
* Change Controller: IETF Change Controller: IETF
* Specification Document(s): Section 4.2 of [RFC8693] Specification Document(s): Section 4.2 of [RFC8693]
8.15. Media Type Registrations 8.15. Media Type Registration
This specification registers the 'application/ace+cbor' media type This specification registers the "application/ace+cbor" media type
for messages of the protocols defined in this document carrying for messages of the protocols defined in this document carrying
parameters encoded in CBOR. This registration follows the procedures parameters encoded in CBOR. This registration follows the procedures
specified in [RFC6838]. specified in [RFC6838].
Type name: application Type name: application
Subtype name: ace+cbor Subtype name: ace+cbor
Required parameters: N/A Required parameters: N/A
Optional parameters: N/A Optional parameters: N/A
Encoding considerations: Must be encoded as CBOR map containing the Encoding considerations: Must be encoded as a CBOR map containing
protocol parameters defined in [this document]. the protocol parameters defined in RFC 9200.
Security considerations: See Section 6 of [this document] Security considerations: See Section 6 of RFC 9200
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: [this document] Published specification: RFC 9200
Applications that use this media type: The type is used by Applications that use this media type: The type is used by
authorization servers, clients and resource servers that support the authorization servers, clients, and resource servers that support
ACE framework with CBOR encoding as specified in [this document]. the ACE framework with CBOR encoding, as specified in RFC 9200.
Fragment identifier considerations: N/A Fragment identifier considerations: N/A
Additional information: N/A Additional information: N/A
Person & email address to contact for further information: Person & email address to contact for further information:
<iesg@ietf.org> IESG <iesg@ietf.org>
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: none Restrictions on usage: none
Author: Ludwig Seitz <ludwig.seitz@combitech.se> Author: Ludwig Seitz <ludwig.seitz@combitech.se>
Change controller: IETF Change controller: IETF
8.16. CoAP Content-Format Registry 8.16. CoAP Content-Format Registry
This specification registers the following entry to the "CoAP The following entry has been registered in the "CoAP Content-Formats"
Content-Formats" registry: registry:
Media Type: application/ace+cbor
Encoding: -
ID: TBD (suggested: 19)
Reference: [this document] Media Type: application/ace+cbor
Encoding: -
ID: 19
Reference: RFC 9200
8.17. Expert Review Instructions 8.17. Expert Review Instructions
All of the IANA registries established in this document are defined All of the IANA registries established in this document are defined
to use a registration policy of Expert Review. This section gives to use a registration policy of Expert Review. This section gives
some general guidelines for what the experts should be looking for, some general guidelines for what the experts should be looking for,
but they are being designated as experts for a reason, so they should but they are being designated as experts for a reason, so they should
be given substantial latitude. be given substantial latitude.
Expert reviewers should take into consideration the following points: Expert Reviewers should take into consideration the following points:
* Point squatting should be discouraged. Reviewers are encouraged * Point squatting should be discouraged. Reviewers are encouraged
to get sufficient information for registration requests to ensure to get sufficient information for registration requests to ensure
that the usage is not going to duplicate one that is already that the usage is not going to duplicate one that is already
registered, and that the point is likely to be used in registered and that the point is likely to be used in deployments.
deployments. The zones tagged as private use are intended for The zones tagged as Private Use are intended for testing purposes
testing purposes and closed environments; code points in other and closed environments; code points in other ranges should not be
ranges should not be assigned for testing. assigned for testing.
* Specifications are needed for the first-come, first-serve range if * Specifications are needed for the first-come, first-serve range if
they are expected to be used outside of closed environments in an they are expected to be used outside of closed environments in an
interoperable way. When specifications are not provided, the interoperable way. When specifications are not provided, the
description provided needs to have sufficient information to description provided needs to have sufficient information to
identify what the point is being used for. identify what the point is being used for.
* Experts should take into account the expected usage of fields when * Experts should take into account the expected usage of fields when
approving point assignment. The fact that there is a range for approving point assignment. The fact that there is a range for
standards track documents does not mean that a standards track Standards Track documents does not mean that a Standards Track
document cannot have points assigned outside of that range. The document cannot have points assigned outside of that range. The
length of the encoded value should be weighed against how many length of the encoded value should be weighed against how many
code points of that length are left, the size of device it will be code points of that length are left, i.e., the size of device it
used on. will be used on.
* Since a high degree of overlap is expected between these * Since a high degree of overlap is expected between these
registries and the contents of the OAuth parameters registries and the contents of the OAuth parameters
[IANA.OAuthParameters] registries, experts should require new [IANA.OAuthParameters] registries, experts should require new
registrations to maintain alignment with parameters from OAuth registrations to maintain alignment with parameters from OAuth
that have comparable functionality. Deviation from this alignment that have comparable functionality. Deviation from this alignment
should only be allowed if there are functional differences, that should only be allowed if there are functional differences that
are motivated by the use case and that cannot be easily or are motivated by the use case and that cannot be easily or
efficiently addressed by comparable OAuth parameters. efficiently addressed by comparable OAuth parameters.
9. Acknowledgments 9. References
This document is a product of the ACE working group of the IETF.
Thanks to Eve Maler for her contributions to the use of OAuth 2.0 and
UMA in IoT scenarios, Robert Taylor for his discussion input, and
Malisa Vucinic for his input on the predecessors of this proposal.
Thanks to the authors of draft-ietf-oauth-pop-key-distribution, from
where parts of the security considerations where copied.
Thanks to Stefanie Gerdes, Olaf Bergmann, and Carsten Bormann for
contributing their work on AS discovery from draft-gerdes-ace-dcaf-
authorize (see Section 5.1) and the considerations on multiple access
tokens.
Thanks to Jim Schaad and Mike Jones for their comprehensive reviews.
Thanks to Benjamin Kaduk for his input on various questions related
to this work.
Thanks to Cigdem Sengul for some very useful review comments.
Thanks to Carsten Bormann for contributing the text for the CoRE
Resource Type registry.
Thanks to Roman Danyliw for suggesting the Appendix E (including its
contents).
Ludwig Seitz and Goeran Selander worked on this document as part of
the CelticPlus project CyberWI, with funding from Vinnova. Ludwig
Seitz was also received further funding for this work by Vinnova in
the context of the CelticNext project Critisec.
10. References
10.1. Normative References
[I-D.ietf-ace-oauth-params] 9.1. Normative References
Seitz, L., "Additional OAuth Parameters for Authorization
in Constrained Environments (ACE)", Work in Progress,
Internet-Draft, draft-ietf-ace-oauth-params-15, 6 May
2021, <https://www.ietf.org/archive/id/draft-ietf-ace-
oauth-params-15.txt>.
[IANA.CborWebTokenClaims] [IANA.CborWebTokenClaims]
IANA, "CBOR Web Token (CWT) Claims", IANA, "CBOR Web Token (CWT) Claims",
<https://www.iana.org/assignments/cwt/cwt.xhtml#claims- <https://www.iana.org/assignments/cwt>.
registry>.
[IANA.CoreParameters] [IANA.CoreParameters]
IANA, "Constrained RESTful Environments (CoRE) IANA, "Constrained RESTful Environments (CoRE)
Parameters", <https://www.iana.org/assignments/core- Parameters",
parameters/core-parameters.xhtml>. <https://www.iana.org/assignments/core-parameters>.
[IANA.JsonWebTokenClaims] [IANA.JsonWebTokenClaims]
IANA, "JSON Web Token Claims", IANA, "JSON Web Token Claims",
<https://www.iana.org/assignments/jwt/jwt.xhtml#claims>. <https://www.iana.org/assignments/jwt>.
[IANA.OAuthAccessTokenTypes] [IANA.OAuthAccessTokenTypes]
IANA, "OAuth Access Token Types", IANA, "OAuth Access Token Types",
<https://www.iana.org/assignments/oauth-parameters/oauth- <https://www.iana.org/assignments/oauth-parameters>.
parameters.xhtml#token-types>.
[IANA.OAuthExtensionsErrorRegistry] [IANA.OAuthExtensionsErrorRegistry]
IANA, "OAuth Extensions Error Registry", IANA, "OAuth Extensions Error Registry",
<https://www.iana.org/assignments/oauth-parameters/oauth- <https://www.iana.org/assignments/oauth-parameters>.
parameters.xhtml#extensions-error>.
[IANA.OAuthParameters] [IANA.OAuthParameters]
IANA, "OAuth Parameters", IANA, "OAuth Parameters",
<https://www.iana.org/assignments/oauth-parameters/oauth- <https://www.iana.org/assignments/oauth-parameters>.
parameters.xhtml#parameters>.
[IANA.TokenIntrospectionResponse] [IANA.TokenIntrospectionResponse]
IANA, "OAuth Token Introspection Response", IANA, "OAuth Token Introspection Response",
<https://www.iana.org/assignments/oauth-parameters/oauth- <https://www.iana.org/assignments/oauth-parameters>.
parameters.xhtml#token-introspection-response>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>. January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012, RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>. <https://www.rfc-editor.org/info/rfc6749>.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization [RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750, Framework: Bearer Token Usage", RFC 6750,
skipping to change at page 63, line 20 skipping to change at line 2946
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H. [RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/info/rfc8747>. 2020, <https://www.rfc-editor.org/info/rfc8747>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949, Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020, DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>. <https://www.rfc-editor.org/info/rfc8949>.
10.2. Informative References [RFC9201] Seitz, L., "Additional OAuth Parameters for Authentication
and Authorization in Constrained Environments (ACE)",
RFC 9201, DOI 10.17487/RFC9201, March 2022,
<https://www.rfc-editor.org/info/rfc9201>.
[BLE] Bluetooth SIG, "Bluetooth Core Specification v5.1", 9.2. Informative References
Section 4.4, January 2019,
[BLE] Bluetooth Special Interest Group, "Core Specification
5.3", Section 4.4, July 2021,
<https://www.bluetooth.com/specifications/bluetooth-core- <https://www.bluetooth.com/specifications/bluetooth-core-
specification/>. specification/>.
[I-D.erdtman-ace-rpcc] [DCAF] Gerdes, S., Bergmann, O., and C. Bormann, "Delegated CoAP
Seitz, L. and S. Erdtman, "Raw-Public-Key and Pre-Shared- Authentication and Authorization Framework (DCAF)", Work
Key as OAuth client credentials", Work in Progress, in Progress, Internet-Draft, draft-gerdes-ace-dcaf-
Internet-Draft, draft-erdtman-ace-rpcc-02, 30 October authorize-04, 19 October 2015,
2017, <https://www.ietf.org/archive/id/draft-erdtman-ace- <https://datatracker.ietf.org/doc/html/draft-gerdes-ace-
rpcc-02.txt>. dcaf-authorize-04>.
[I-D.ietf-ace-dtls-authorize]
Gerdes, S., Bergmann, O., Bormann, C., Selander, G., and
L. Seitz, "Datagram Transport Layer Security (DTLS)
Profile for Authentication and Authorization for
Constrained Environments (ACE)", Work in Progress,
Internet-Draft, draft-ietf-ace-dtls-authorize-18, 4 June
2021, <https://www.ietf.org/archive/id/draft-ietf-ace-
dtls-authorize-18.txt>.
[I-D.ietf-ace-oscore-profile]
Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"OSCORE Profile of the Authentication and Authorization
for Constrained Environments Framework", Work in Progress,
Internet-Draft, draft-ietf-ace-oscore-profile-19, 6 May
2021, <https://www.ietf.org/archive/id/draft-ietf-ace-
oscore-profile-19.txt>.
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", Work in Progress, Internet-Draft,
draft-ietf-quic-transport-34, 14 January 2021,
<https://www.ietf.org/archive/id/draft-ietf-quic-
transport-34.txt>.
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
dtls13-43, 30 April 2021, <https://www.ietf.org/internet-
drafts/draft-ietf-tls-dtls13-43.txt>.
[Margi10impact] [Margi10impact]
Margi, C. B., de Oliveira, B.T., de Sousa, G.T., Simplicio Margi, C., de Oliveira, B., de Sousa, G., Simplicio Jr,
Jr, M.A., Barreto, P.S.L.M., Carvalho, T.C.M.B., Naeslund, M., Barreto, P., Carvalho, T., Naeslund, M., and R. Gold,
M., and R. Gold, "Impact of Operating Systems on Wireless "Impact of Operating Systems on Wireless Sensor Networks
Sensor Networks (Security) Applications and Testbeds", (Security) Applications and Testbeds", Proceedings of the
Proceedings of the 19th International Conference on 19th International Conference on Computer Communications
Computer Communications and Networks (ICCCN), August 2010. and Networks, DOI 10.1109/ICCCN.2010.5560028, August 2010,
<https://doi.org/10.1109/ICCCN.2010.5560028>.
[MQTT5.0] Banks, A., Briggs, E., Borgendale, K., and R. Gupta, "MQTT [MQTT5.0] Banks, A., Briggs, E., Borgendale, K., and R. Gupta, "MQTT
Version 5.0", OASIS Standard, March 2019, Version 5.0", OASIS Standard, March 2019,
<https://docs.oasis-open.org/mqtt/mqtt/v5.0/mqtt- <https://docs.oasis-open.org/mqtt/mqtt/v5.0/mqtt-
v5.0.html>. v5.0.html>.
[OAUTH-RPCC]
Seitz, L., Erdtman, S., and M. Tiloca, "Raw-Public-Key and
Pre-Shared-Key as OAuth client credentials", Work in
Progress, Internet-Draft, draft-erdtman-oauth-rpcc-00, 21
November 2017, <https://datatracker.ietf.org/doc/html/
draft-erdtman-oauth-rpcc-00>.
[POP-KEY-DIST]
Bradley, J., Hunt, P., Jones, M., Tschofenig, H., and M.
Meszaros, "OAuth 2.0 Proof-of-Possession: Authorization
Server to Client Key Distribution", Work in Progress,
Internet-Draft, draft-ietf-oauth-pop-key-distribution-07,
27 March 2019, <https://datatracker.ietf.org/doc/html/
draft-ietf-oauth-pop-key-distribution-07>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", [RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>. <https://www.rfc-editor.org/info/rfc4949>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>. <https://www.rfc-editor.org/info/rfc6690>.
[RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0 [RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0
Threat Model and Security Considerations", RFC 6819, Threat Model and Security Considerations", RFC 6819,
skipping to change at page 66, line 29 skipping to change at line 3085
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments "Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>. <https://www.rfc-editor.org/info/rfc8613>.
[RFC8628] Denniss, W., Bradley, J., Jones, M., and H. Tschofenig, [RFC8628] Denniss, W., Bradley, J., Jones, M., and H. Tschofenig,
"OAuth 2.0 Device Authorization Grant", RFC 8628, "OAuth 2.0 Device Authorization Grant", RFC 8628,
DOI 10.17487/RFC8628, August 2019, DOI 10.17487/RFC8628, August 2019,
<https://www.rfc-editor.org/info/rfc8628>. <https://www.rfc-editor.org/info/rfc8628>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, March 2022,
<https://www.rfc-editor.org/info/rfc9147>.
[RFC9202] Gerdes, S., Bergmann, O., Bormann, C., Selander, G., and
L. Seitz, "Datagram Transport Layer Security (DTLS)
Profile for Authentication and Authorization for
Constrained Environments (ACE)", RFC 9202,
DOI 10.17487/RFC9202, March 2022,
<https://www.rfc-editor.org/info/rfc9202>.
[RFC9203] Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"The Object Security for Constrained RESTful Environments
(OSCORE) Profile of the Authentication and Authorization
for Constrained Environments (ACE) Framework", RFC 9203,
DOI 10.17487/RFC9203, March 2022,
<https://www.rfc-editor.org/info/rfc9203>.
Appendix A. Design Justification Appendix A. Design Justification
This section provides further insight into the design decisions of This section provides further insight into the design decisions of
the solution documented in this document. Section 3 lists several the solution documented in this document. Section 3 lists several
building blocks and briefly summarizes their importance. The building blocks and briefly summarizes their importance. The
justification for offering some of those building blocks, as opposed justification for offering some of those building blocks, as opposed
to using OAuth 2.0 as is, is given below. to using OAuth 2.0 as is, is given below.
Common IoT constraints are: Common IoT constraints are:
Low Power Radio: Low Power Radio:
Many IoT devices are equipped with a small battery that needs to
Many IoT devices are equipped with a small battery which needs to
last for a long time. For many constrained wireless devices, the last for a long time. For many constrained wireless devices, the
highest energy cost is associated to transmitting or receiving highest energy cost is associated to transmitting or receiving
messages (roughly by a factor of 10 compared to AES) messages (roughly by a factor of 10 compared to AES)
[Margi10impact]. It is therefore important to keep the total [Margi10impact]. It is therefore important to keep the total
communication overhead low, including minimizing the number and communication overhead low, including minimizing the number and
size of messages sent and received, which has an impact of choice size of messages sent and received, which has an impact of choice
on the message format and protocol. By using CoAP over UDP and on the message format and protocol. By using CoAP over UDP and
CBOR encoded messages, some of these aspects are addressed. CBOR-encoded messages, some of these aspects are addressed.
Security protocols contribute to the communication overhead and Security protocols contribute to the communication overhead and
can, in some cases, be optimized. For example, authentication and can, in some cases, be optimized. For example, authentication and
key establishment may, in certain cases where security key establishment may, in certain cases where security
requirements allow, be replaced by provisioning of security requirements allow, be replaced by the provisioning of security
context by a trusted third party, using transport or application- context by a trusted third party, using transport or application-
layer security. layer security.
Low CPU Speed: Low CPU Speed:
Some IoT devices are equipped with processors that are Some IoT devices are equipped with processors that are
significantly slower than those found in most current devices on significantly slower than those found in most current devices on
the Internet. This typically has implications on what timely the Internet. This typically has implications on what timely
cryptographic operations a device is capable of performing, which cryptographic operations a device is capable of performing, which
in turn impacts, e.g., protocol latency. Symmetric key in turn impacts, e.g., protocol latency. Symmetric key
cryptography may be used instead of the computationally more cryptography may be used instead of the computationally more
expensive public key cryptography where the security requirements expensive public key cryptography where the security requirements
so allow, but this may also require support for trusted-third- so allow, but this may also require support for trusted, third-
party-assisted secret key establishment using transport- or party-assisted secret key establishment using transport- or
application-layer security. application-layer security.
Small Amount of Memory: Small Amount of Memory:
Microcontrollers embedded in IoT devices are often equipped with Microcontrollers embedded in IoT devices are often equipped with
only a small amount of RAM and flash memory, which places only a small amount of RAM and flash memory, which places
limitations on what kind of processing can be performed and how limitations on what kind of processing can be performed and how
much code can be put on those devices. To reduce code size, fewer much code can be put on those devices. To reduce code size, fewer
and smaller protocol implementations can be put on the firmware of and smaller protocol implementations can be put on the firmware of
such a device. In this case, CoAP may be used instead of HTTP, such a device. In this case, CoAP may be used instead of HTTP,
symmetric-key cryptography instead of public-key cryptography, and symmetric-key cryptography may be used instead of public-key
CBOR instead of JSON. An authentication and key establishment cryptography, and CBOR may be used instead of JSON. An
protocol, e.g., the DTLS handshake, in comparison with assisted authentication and key establishment protocol, e.g., the DTLS
key establishment, also has an impact on memory and code handshake, in comparison with assisted key establishment, also
footprints. have an impact on memory and code footprints.
User Interface Limitations: User Interface Limitations:
Protecting access to resources is both an important security as Protecting access to resources is both an important security as
well as privacy feature. End users and enterprise customers may well as privacy feature. End users and enterprise customers may
not want to give access to the data collected by their IoT device not want to give access to the data collected by their IoT device
or to functions it may offer to third parties. Since the or to functions it may offer to third parties. Since the
classical approach of requesting permissions from end users via a classical approach of requesting permissions from end users via a
rich user interface does not work in many IoT deployment rich user interface does not work in many IoT deployment
scenarios, these functions need to be delegated to user-controlled scenarios, these functions need to be delegated to user-controlled
devices that are better suitable for such tasks, such as smart devices that are better suitable for such tasks, such as
phones and tablets. smartphones and tablets.
Communication Constraints: Communication Constraints:
In certain constrained settings an IoT device may not be able to In certain constrained settings, an IoT device may not be able to
communicate with a given device at all times. Devices may be communicate with a given device at all times. Devices may be
sleeping, or just disconnected from the Internet because of sleeping or just disconnected from the Internet because of general
general lack of connectivity in the area, for cost reasons, or for lack of connectivity in the area for cost or security reasons,
security reasons, e.g., to avoid an entry point for Denial-of- e.g., to avoid an entry point for denial-of-service attacks.
Service attacks.
The communication interactions this framework builds upon (as The communication interactions this framework builds upon (as
shown graphically in Figure 1) may be accomplished using a variety shown graphically in Figure 1) may be accomplished using a variety
of different protocols, and not all parts of the message flow are of different protocols, and not all parts of the message flow are
used in all applications due to the communication constraints. used in all applications due to the communication constraints.
Deployments making use of CoAP are expected, but this framework is Deployments making use of CoAP are expected, but this framework is
not limited to them. Other protocols such as HTTP, or even not limited to them. Other protocols, such as HTTP or Bluetooth
protocols such as Bluetooth Smart communication that do not Smart communication, that do not necessarily use IP could also be
necessarily use IP, could also be used. The latter raises the used. The latter raises the need for application-layer security
need for application-layer security over the various interfaces. over the various interfaces.
In the light of these constraints we have made the following design In the light of these constraints, we have made the following design
decisions: decisions:
CBOR, COSE, CWT: CBOR, COSE, CWT:
When using this framework, it is RECOMMENDED to use CBOR [RFC8949] When using this framework, it is RECOMMENDED to use CBOR [RFC8949]
as data format. Where CBOR data needs to be protected, the use of as the data format. Where CBOR data needs to be protected, the
COSE [RFC8152] is RECOMMENDED. Furthermore, where self-contained use of COSE [RFC8152] is RECOMMENDED. Furthermore, where self-
tokens are needed, it is RECOMMENDED to use of CWT [RFC8392]. contained tokens are needed, it is RECOMMENDED to use CWT
These measures aim at reducing the size of messages sent over the [RFC8392]. These measures aim at reducing the size of messages
wire, the RAM size of data objects that need to be kept in memory sent over the wire, the RAM size of data objects that need to be
and the size of libraries that devices need to support. kept in memory, and the size of libraries that devices need to
support.
CoAP: CoAP:
When using this framework, it is RECOMMENDED to use of CoAP When using this framework, it is RECOMMENDED to use CoAP [RFC7252]
[RFC7252] instead of HTTP. This does not preclude the use of instead of HTTP. This does not preclude the use of other
other protocols specifically aimed at constrained devices, like, protocols specifically aimed at constrained devices, e.g.,
e.g., Bluetooth Low Energy (see Section 3.2). This aims again at Bluetooth Low Energy (see Section 3.2). This aims again at
reducing the size of messages sent over the wire, the RAM size of reducing the size of messages sent over the wire, the RAM size of
data objects that need to be kept in memory and the size of data objects that need to be kept in memory, and the size of
libraries that devices need to support. libraries that devices need to support.
Access Information: Access Information:
This framework defines the name "Access Information" for data This framework defines the name "Access Information" for data
concerning the RS that the AS returns to the client in an access concerning the RS that the AS returns to the client in an access
token response (see Section 5.8.2). This aims at enabling token response (see Section 5.8.2). This aims at enabling
scenarios where a powerful client, supporting multiple profiles, scenarios where a powerful client supporting multiple profiles
needs to interact with an RS for which it does not know the needs to interact with an RS for which it does not know the
supported profiles and the raw public key. supported profiles and the raw public key.
Proof-of-Possession:
Proof of Possession:
This framework makes use of proof-of-possession tokens, using the This framework makes use of proof-of-possession tokens, using the
"cnf" claim [RFC8747]. A request parameter "cnf" and a Response "cnf" claim [RFC8747]. A request parameter "cnf" and a Response
parameter "cnf", both having a value space semantically and parameter "cnf", both having a value space semantically and
syntactically identical to the "cnf" claim, are defined for the syntactically identical to the "cnf" claim, are defined for the
token endpoint, to allow requesting and stating confirmation keys. token endpoint to allow requesting and stating confirmation keys.
This aims at making token theft harder. Token theft is This aims at making token theft harder. Token theft is
specifically relevant in constrained use cases, as communication specifically relevant in constrained use cases, as communication
often passes through middle-boxes, which could be able to steal often passes through middleboxes, which could be able to steal
bearer tokens and use them to gain unauthorized access. bearer tokens and use them to gain unauthorized access.
Authz-Info endpoint: Authz-Info endpoint:
This framework introduces a new way of providing access tokens to This framework introduces a new way of providing access tokens to
an RS by exposing a authz-info endpoint, to which access tokens an RS by exposing an authz-info endpoint to which access tokens
can be POSTed. This aims at reducing the size of the request can be POSTed. This aims at reducing the size of the request
message and the code complexity at the RS. The size of the message and the code complexity at the RS. The size of the
request message is problematic, since many constrained protocols request message is problematic, since many constrained protocols
have severe message size limitations at the physical layer (e.g., have severe message size limitations at the physical layer (e.g.,
in the order of 100 bytes). This means that larger packets get in the order of 100 bytes). This means that larger packets get
fragmented, which in turn combines badly with the high rate of fragmented, which in turn combines badly with the high rate of
packet loss, and the need to retransmit the whole message if one packet loss and the need to retransmit the whole message if one
packet gets lost. Thus separating sending of the request and packet gets lost. Thus, separating sending of the request and
sending of the access tokens helps to reduce fragmentation. sending of the access tokens helps to reduce fragmentation.
Client Credentials Grant: Client Credentials Grant:
In this framework the use of the client credentials grant is In this framework, the use of the client credentials grant is
RECOMMENDED for machine-to-machine communication use cases, where RECOMMENDED for machine-to-machine communication use cases, where
manual intervention of the resource owner to produce a grant token manual intervention of the resource owner to produce a grant token
is not feasible. The intention is that the resource owner would is not feasible. The intention is that the resource owner would
instead pre-arrange authorization with the AS, based on the instead prearrange authorization with the AS based on the client's
client's own credentials. The client can then (without manual own credentials. The client can then (without manual
intervention) obtain access tokens from the AS. intervention) obtain access tokens from the AS.
Introspection: Introspection:
In this framework the use of access token introspection is In this framework, the use of access token introspection is
RECOMMENDED in cases where the client is constrained in a way that RECOMMENDED in cases where the client is constrained in a way that
it can not easily obtain new access tokens (i.e. it has it cannot easily obtain new access tokens (i.e., it has
connectivity issues that prevent it from communicating with the connectivity issues that prevent it from communicating with the
AS). In that case it is RECOMMENDED to use a long-term token, AS). In that case, it is RECOMMENDED to use a long-term token
that could be a simple reference. The RS is assumed to be able to that could be a simple reference. The RS is assumed to be able to
communicate with the AS, and can therefore perform introspection, communicate with the AS and can therefore perform introspection in
in order to learn the claims associated with the token reference. order to learn the claims associated with the token reference.
The advantage of such an approach is that the resource owner can The advantage of such an approach is that the resource owner can
change the claims associated to the token reference without having change the claims associated to the token reference without having
to be in contact with the client, thus granting or revoking access to be in contact with the client, thus granting or revoking access
rights. rights.
Appendix B. Roles and Responsibilities Appendix B. Roles and Responsibilities
Resource Owner Resource Owner
* Make sure that the RS is registered at the AS. This includes * Make sure that the RS is registered at the AS. This includes
making known to the AS which profiles, token_type, scopes, and making known to the AS which profiles, token_type, scopes, and
skipping to change at page 70, line 7 skipping to change at line 3277
Resource Owner Resource Owner
* Make sure that the RS is registered at the AS. This includes * Make sure that the RS is registered at the AS. This includes
making known to the AS which profiles, token_type, scopes, and making known to the AS which profiles, token_type, scopes, and
key types (symmetric/asymmetric) the RS supports. Also making key types (symmetric/asymmetric) the RS supports. Also making
it known to the AS which audience(s) the RS identifies itself it known to the AS which audience(s) the RS identifies itself
with. with.
* Make sure that clients can discover the AS that is in charge of * Make sure that clients can discover the AS that is in charge of
the RS. the RS.
* If the client-credentials grant is used, make sure that the AS * If the client-credentials grant is used, make sure that the AS
has the necessary, up-to-date, access control policies for the has the necessary, up-to-date access control policies for the
RS. RS.
Requesting Party Requesting Party
* Make sure that the client is provisioned the necessary * Make sure that the client is provisioned the necessary
credentials to authenticate to the AS. credentials to authenticate to the AS.
* Make sure that the client is configured to follow the security * Make sure that the client is configured to follow the security
requirements of the Requesting Party when issuing requests requirements of the requesting party when issuing requests
(e.g., minimum communication security requirements, trust (e.g., minimum communication security requirements or trust
anchors). anchors).
* Register the client at the AS. This includes making known to * Register the client at the AS. This includes making known to
the AS which profiles, token_types, and key types (symmetric/ the AS which profiles, token_types, and key types (symmetric/
asymmetric) the client. asymmetric) for the client.
Authorization Server Authorization Server
* Register the RS and manage corresponding security contexts. * Register the RS and manage corresponding security contexts.
* Register clients and authentication credentials. * Register clients and authentication credentials.
* Allow Resource Owners to configure and update access control
* Allow resource owners to configure and update access control
policies related to their registered RSs. policies related to their registered RSs.
* Expose the token endpoint to allow clients to request tokens. * Expose the token endpoint to allow clients to request tokens.
* Authenticate clients that wish to request a token. * Authenticate clients that wish to request a token.
* Process a token request using the authorization policies * Process a token request using the authorization policies
configured for the RS. configured for the RS.
* Optionally: Expose the introspection endpoint that allows RS's
* Optionally, expose the introspection endpoint that allows RSs
to submit token introspection requests. to submit token introspection requests.
* If providing an introspection endpoint: Authenticate RSs that
* If providing an introspection endpoint, authenticate RSs that
wish to get an introspection response. wish to get an introspection response.
* If providing an introspection endpoint: Process token
* If providing an introspection endpoint, process token
introspection requests. introspection requests.
* Optionally: Handle token revocation.
* Optionally: Provide discovery metadata. See [RFC8414] * Optionally, handle token revocation.
* Optionally: Handle refresh tokens.
* Optionally, provide discovery metadata. See [RFC8414].
* Optionally, handle refresh tokens.
Client Client
* Discover the AS in charge of the RS that is to be targeted with * Discover the AS in charge of the RS that is to be targeted with
a request. a request.
* Submit the token request (see step (A) of Figure 1). * Submit the token request (see step (A) of Figure 1).
- Authenticate to the AS. - Authenticate to the AS.
- Optionally (if not pre-configured): Specify which RS, which
- Optionally (if not preconfigured), specify which RS, which
resource(s), and which action(s) the request(s) will target. resource(s), and which action(s) the request(s) will target.
- If raw public keys (rpk) or certificates are used, make sure
the AS has the right rpk or certificate for this client. - If raw public keys (RPKs) or certificates are used, make
sure the AS has the right RPK or certificate for this
client.
* Process the access token and Access Information (see step (B) * Process the access token and Access Information (see step (B)
of Figure 1). of Figure 1).
- Check that the Access Information provides the necessary - Check that the Access Information provides the necessary
security parameters (e.g., PoP key, information on security parameters (e.g., PoP key or information on
communication security protocols supported by the RS). communication security protocols supported by the RS).
- Safely store the proof-of-possession key. - Safely store the proof-of-possession key.
- If provided by the AS: Safely store the refresh token. - If provided by the AS, safely store the refresh token.
* Send the token and request to the RS (see step (C) of * Send the token and request to the RS (see step (C) of
Figure 1). Figure 1).
- Authenticate towards the RS (this could coincide with the - Authenticate towards the RS (this could coincide with the
proof of possession process). proof-of-possession process).
- Transmit the token as specified by the AS (default is to the - Transmit the token as specified by the AS (default is to the
authz-info endpoint, alternative options are specified by authz-info endpoint; alternative options are specified by
profiles). profiles).
- Perform the proof-of-possession procedure as specified by - Perform the proof-of-possession procedure as specified by
the profile in use (this may already have been taken care of the profile in use (this may already have been taken care of
through the authentication procedure). through the authentication procedure).
* Process the RS response (see step (F) of Figure 1) of the RS. * Process the RS response (see step (F) of Figure 1) of the RS.
Resource Server Resource Server
* Expose a way to submit access tokens. By default this is the * Expose a way to submit access tokens. By default, this is the
authz-info endpoint. authz-info endpoint.
* Process an access token. * Process an access token.
- Verify the token is from a recognized AS. - Verify the token is from a recognized AS.
- Check the token's integrity. - Check the token's integrity.
- Verify that the token applies to this RS. - Verify that the token applies to this RS.
- Check that the token has not expired (if the token provides - Check that the token has not expired (if the token provides
expiration information). expiration information).
- Store the token so that it can be retrieved in the context - Store the token so that it can be retrieved in the context
of a matching request. of a matching request.
Note: The order proposed here is not normative, any process
Note: The order proposed here is not normative; any process
that arrives at an equivalent result can be used. A noteworthy that arrives at an equivalent result can be used. A noteworthy
consideration is whether one can use cheap operations early on consideration is whether one can use cheap operations early on
to quickly discard non-applicable or invalid tokens, before to quickly discard nonapplicable or invalid tokens before
performing expensive cryptographic operations (e.g. doing an performing expensive cryptographic operations (e.g., doing an
expiration check before verifying a signature). expiration check before verifying a signature).
* Process a request. * Process a request.
- Set up communication security with the client. - Set up communication security with the client.
- Authenticate the client. - Authenticate the client.
- Match the client against existing tokens. - Match the client against existing tokens.
- Check that tokens belonging to the client actually authorize - Check that tokens belonging to the client actually authorize
the requested action. the requested action.
- Optionally: Check that the matching tokens are still valid,
- Optionally, check that the matching tokens are still valid,
using introspection (if this is possible.) using introspection (if this is possible.)
* Send a response following the agreed upon communication * Send a response following the agreed upon communication
security mechanism(s). security mechanism(s).
* Safely store credentials such as raw public keys for
* Safely store credentials, such as raw public keys, for
authentication or proof-of-possession keys linked to access authentication or proof-of-possession keys linked to access
tokens. tokens.
Appendix C. Requirements on Profiles Appendix C. Requirements on Profiles
This section lists the requirements on profiles of this framework, This section lists the requirements on profiles of this framework for
for the convenience of profile designers. the convenience of profile designers.
* Optionally, define new methods for the client to discover the
necessary permissions and AS for accessing a resource different
from the one proposed in Sections 5.1 and 4
* Optionally, specify new grant types (Section 5.4).
* Optionally, define the use of client certificates as client
credential type (Section 5.5).
* Specify the communication protocol the client and RS must use
(e.g., CoAP) (Sections 5 and 5.8.4.3).
* Optionally define new methods for the client to discover the
necessary permissions and AS for accessing a resource, different
from the one proposed in Section 5.1. Section 4
* Optionally specify new grant types. Section 5.4
* Optionally define the use of client certificates as client
credential type. Section 5.5
* Specify the communication protocol the client and RS the must use
(e.g., CoAP). Section 5 and Section 5.8.4.3
* Specify the security protocol the client and RS must use to * Specify the security protocol the client and RS must use to
protect their communication (e.g., OSCORE or DTLS). This must protect their communication (e.g., OSCORE or DTLS). This must
provide encryption, integrity and replay protection. provide encryption and integrity and replay protection
Section 5.8.4.3 (Section 5.8.4.3).
* Specify how the client and the RS mutually authenticate.
Section 4 * Specify how the client and the RS mutually authenticate
* Specify the proof-of-possession protocol(s) and how to select one, (Section 4).
* Specify the proof-of-possession protocol(s) and how to select one
if several are available. Also specify which key types (e.g., if several are available. Also specify which key types (e.g.,
symmetric/asymmetric) are supported by a specific proof-of- symmetric/asymmetric) are supported by a specific proof-of-
possession protocol. Section 5.8.4.2 possession protocol (Section 5.8.4.2).
* Specify a unique ace_profile identifier. Section 5.8.4.3
* If introspection is supported: Specify the communication and * Specify a unique ace_profile identifier (Section 5.8.4.3).
security protocol for introspection. Section 5.9
* If introspection is supported, specify the communication and
security protocol for introspection (Section 5.9).
* Specify the communication and security protocol for interactions * Specify the communication and security protocol for interactions
between client and AS. This must provide encryption, integrity between the client and AS. This must provide encryption,
protection, replay protection and a binding between requests and integrity protection, replay protection, and a binding between
responses. Section 5 and Section 5.8 requests and responses (Sections 5 and 5.8).
* Specify how/if the authz-info endpoint is protected, including how * Specify how/if the authz-info endpoint is protected, including how
error responses are protected. Section 5.10.1 error responses are protected (Section 5.10.1).
* Optionally define other methods of token transport than the authz-
info endpoint. Section 5.10.1
Appendix D. Assumptions on AS Knowledge about C and RS * Optionally, define other methods of token transport than the
authz-info endpoint (Section 5.10.1).
Appendix D. Assumptions on AS Knowledge about the C and RS
This section lists the assumptions on what an AS should know about a This section lists the assumptions on what an AS should know about a
client and an RS in order to be able to respond to requests to the client and an RS in order to be able to respond to requests to the
token and introspection endpoints. How this information is token and introspection endpoints. How this information is
established is out of scope for this document. established is out of scope for this document.
* The identifier of the client or RS. * The identifier of the client or RS.
* The profiles that the client or RS supports. * The profiles that the client or RS supports.
* The scopes that the RS supports. * The scopes that the RS supports.
* The audiences that the RS identifies with. * The audiences that the RS identifies with.
* The key types (e.g., pre-shared symmetric key, raw public key, key * The key types (e.g., pre-shared symmetric key, raw public key, key
length, other key parameters) that the client or RS supports. length, and other key parameters) that the client or RS supports.
* The types of access tokens the RS supports (e.g., CWT). * The types of access tokens the RS supports (e.g., CWT).
* If the RS supports CWTs, the COSE parameters for the crypto * If the RS supports CWTs, the COSE parameters for the crypto
wrapper (e.g., algorithm, key-wrap algorithm, key-length) that the wrapper (e.g., algorithm, key-wrap algorithm, and key-length) that
RS supports. the RS supports.
* The expiration time for access tokens issued to this RS (unless * The expiration time for access tokens issued to this RS (unless
the RS accepts a default time chosen by the AS). the RS accepts a default time chosen by the AS).
* The symmetric key shared between client and AS (if any).
* The symmetric key shared between RS and AS (if any). * The symmetric key shared between the client and AS (if any).
* The symmetric key shared between the RS and AS (if any).
* The raw public key of the client or RS (if any). * The raw public key of the client or RS (if any).
* Whether the RS has synchronized time (and thus is able to use the * Whether the RS has synchronized time (and thus is able to use the
'exp' claim) or not. 'exp' claim) or not.
Appendix E. Differences to OAuth 2.0 Appendix E. Differences to OAuth 2.0
This document adapts OAuth 2.0 to be suitable for constrained This document adapts OAuth 2.0 to be suitable for constrained
environments. This sections lists the main differences from the environments. This section lists the main differences from the
normative requirements of OAuth 2.0. normative requirements of OAuth 2.0.
* Use of TLS -- OAuth 2.0 requires the use of TLS both to protect Use of TLS
the communication between AS and client when requesting an access OAuth 2.0 requires the use of TLS to protect the communication
token; between client and RS when accessing a resource and between between the AS and client when requesting an access token, between
AS and RS if introspection is used. This framework requires the client and RS when accessing a resource, and between the AS
similar security properties, but does not require that they be and RS if introspection is used. This framework requires similar
realized with TLS. See Section 5. security properties but does not require that they be realized
* Cardinality of "grant_type" parameter -- In client-to-AS requests with TLS. See Section 5.
using OAuth 2.0, the "grant_type" parameter is required (per
[RFC6749]). In this framework, this parameter is optional. See Cardinality of "grant_type" parameter
Section 5.8.1. In client-to-AS requests using OAuth 2.0, the "grant_type"
* Encoding of "scope" parameter -- In client-to-AS requests using parameter is required (per [RFC6749]). In this framework, this
OAuth 2.0, the "scope" parameter is string encoded (per parameter is optional. See Section 5.8.1.
[RFC6749]). In this framework, this parameter may also be encoded
as a byte string. See Section 5.8.1. Encoding of "scope" parameter
* Cardinality of "token_type" parameter -- in AS-to-client responses In client-to-AS requests using OAuth 2.0, the "scope" parameter is
using OAuth 2.0, the token_type parameter is required (per string encoded (per [RFC6749]). In this framework, this parameter
[RFC6749]). In this framework, this parameter is optional. See may also be encoded as a byte string. See Section 5.8.1.
Section 5.8.2.
* Access token retention -- in OAuth 2.0, the access token may be Cardinality of "token_type" parameter
sent with every request to the RS. The exact use of access tokens In AS-to-client responses using OAuth 2.0, the token_type
depends on the semantics of the application and the session parameter is required (per [RFC6749]). In this framework, this
management concept it uses. In this framework, the RS must be parameter is optional. See Section 5.8.2.
able to store these tokens for later use. See Section 5.10.1.
Access token retention
In OAuth 2.0, the access token may be sent with every request to
the RS. The exact use of access tokens depends on the semantics
of the application and the session management concept it uses. In
this framework, the RS must be able to store these tokens for
later use. See Section 5.10.1.
Appendix F. Deployment Examples Appendix F. Deployment Examples
There is a large variety of IoT deployments, as is indicated in There is a large variety of IoT deployments, as is indicated in
Appendix A, and this section highlights a few common variants. This Appendix A, and this section highlights a few common variants. This
section is not normative but illustrates how the framework can be section is not normative but illustrates how the framework can be
applied. applied.
For each of the deployment variants, there are a number of possible For each of the deployment variants, there are a number of possible
security setups between clients, resource servers and authorization security setups between clients, resource servers, and authorization
servers. The main focus in the following subsections is on how servers. The main focus in the following subsections is on how
authorization of a client request for a resource hosted by an RS is authorization of a client request for a resource hosted by an RS is
performed. This requires the security of the requests and responses performed. This requires the security of the requests and responses
between the clients and the RS to be considered. between the clients and the RS to be considered.
Note: CBOR diagnostic notation is used for examples of requests and Note: CBOR diagnostic notation is used for examples of requests and
responses. responses.
F.1. Local Token Validation F.1. Local Token Validation
In this scenario, the case where the resource server is offline is In this scenario, the case where the resource server is offline is
considered, i.e., it is not connected to the AS at the time of the considered, i.e., it is not connected to the AS at the time of the
access request. This access procedure involves steps A, B, C, and F access request. This access procedure involves steps (A), (B), (C),
of Figure 1. and (F) of Figure 1.
Since the resource server must be able to verify the access token Since the resource server must be able to verify the access token
locally, self-contained access tokens must be used. locally, self-contained access tokens must be used.
This example shows the interactions between a client, the This example shows the interactions between a client, the
authorization server and a temperature sensor acting as a resource authorization server, and a temperature sensor acting as a resource
server. Message exchanges A and B are shown in Figure 17. server. Message exchanges A and B are shown in Figure 11.
A: The client first generates a public-private key pair used for A: The client first generates a public-private key pair used for
communication security with the RS. communication security with the RS.
The client sends a CoAP POST request to the token endpoint at the
AS. The security of this request can be transport or application The client sends a CoAP POST request to the token endpoint at the
layer. It is up the communication security profile to define. In AS. The security of this request can be transport or application
the example it is assumed that both client and AS have performed layer. It is up the communication security profile to define.
mutual authentication e.g. via DTLS. The request contains the In the example, it is assumed that both the client and AS have
public key of the client and the Audience parameter set to performed mutual authentication, e.g., via DTLS. The request
"tempSensorInLivingRoom", a value that the temperature sensor contains the public key of the client and the audience parameter
identifies itself with. The AS evaluates the request and set to "tempSensorInLivingRoom", a value that the temperature
authorizes the client to access the resource. sensor identifies itself with. The AS evaluates the request and
B: The AS responds with a 2.05 Content response containing the authorizes the client to access the resource.
Access Information, including the access token. The PoP access
token contains the public key of the client, and the Access B: The AS responds with a 2.05 (Content) response containing the
Information contains the public key of the RS. For communication Access Information, including the access token. The PoP access
security this example uses DTLS RawPublicKey between the client token contains the public key of the client, and the Access
and the RS. The issued token will have a short validity time, Information contains the public key of the RS. For communication
i.e., "exp" close to "iat", in order to mitigate attacks using security, this example uses DTLS RawPublicKey between the client
stolen client credentials. The token includes the claim such as and the RS. The issued token will have a short validity time,
"scope" with the authorized access that an owner of the i.e., "exp" close to "iat", in order to mitigate attacks using
temperature device can enjoy. In this example, the "scope" claim, stolen client credentials. The token includes claims, such as
issued by the AS, informs the RS that the owner of the token, that "scope", with the authorized access that an owner of the
can prove the possession of a key is authorized to make a GET temperature device can enjoy. In this example, the "scope" claim
request against the /temperature resource and a POST request on issued by the AS informs the RS that the owner of the token that
the /firmware resource. Note that the syntax and semantics of the can prove the possession of a key is authorized to make a GET
scope claim are application specific. request against the /temperature resource and a POST request on
Note: In this example it is assumed that the client knows what the /firmware resource. Note that the syntax and semantics of
resource it wants to access, and is therefore able to request the scope claim are application specific.
specific audience and scope claims for the access token.
Note: In this example, it is assumed that the client knows what
resource it wants to access and is therefore able to request
specific audience and scope claims for the access token.
Authorization Authorization
Client Server Client Server
| | | |
|<=======>| DTLS Connection Establishment |<=======>| DTLS Connection Establishment
| | and mutual authentication | | and mutual authentication
| | | |
A: +-------->| Header: POST (Code=0.02) A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"token" | POST | Uri-Path:"token"
| | Content-Format: application/ace+cbor | | Content-Format: application/ace+cbor
| | Payload: <Request-Payload> | | Payload: <Request-Payload>
| | | |
B: |<--------+ Header: 2.05 Content B: |<--------+ Header: 2.05 Content
| 2.05 | Content-Format: application/ace+cbor | 2.05 | Content-Format: application/ace+cbor
| | Payload: <Response-Payload> | | Payload: <Response-Payload>
| | | |
Figure 17: Token Request and Response Using Client Credentials. Figure 11: Token Request and Response Using Client Credentials
The information contained in the Request-Payload and the Response- The information contained in the Request-Payload and the Response-
Payload is shown in Figure 18 Note that the parameter "rs_cnf" from Payload is shown in Figure 12. Note that the parameter "rs_cnf" from
[I-D.ietf-ace-oauth-params] is used to inform the client about the [RFC9201] is used to inform the client about the resource server's
resource server's public key. public key.
Request-Payload : Request-Payload :
{ {
"audience" : "tempSensorInLivingRoom", "audience" : "tempSensorInLivingRoom",
"client_id" : "myclient", "client_id" : "myclient",
"req_cnf" : { "req_cnf" : {
"COSE_Key" : { "COSE_Key" : {
"kid" : b64'1Bg8vub9tLe1gHMzV76e8', "kid" : b64'1Bg8vub9tLe1gHMzV76e8',
"kty" : "EC", "kty" : "EC",
"crv" : "P-256", "crv" : "P-256",
skipping to change at page 76, line 34 skipping to change at line 3647
"COSE_Key" : { "COSE_Key" : {
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk', "kid" : b64'c29tZSBwdWJsaWMga2V5IGlk',
"kty" : "EC", "kty" : "EC",
"crv" : "P-256", "crv" : "P-256",
"x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4', "x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4',
"y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM' "y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM'
} }
} }
} }
Figure 18: Request and Response Payload Details. Figure 12: Request and Response Payload Details
The content of the access token is shown in Figure 19. The content of the access token is shown in Figure 13.
{ {
"aud" : "tempSensorInLivingRoom", "aud" : "tempSensorInLivingRoom",
"iat" : "1563451500", "iat" : "1563451500",
"exp" : "1563453000", "exp" : "1563453000",
"scope" : "temperature_g firmware_p", "scope" : "temperature_g firmware_p",
"cnf" : { "cnf" : {
"COSE_Key" : { "COSE_Key" : {
"kid" : b64'1Bg8vub9tLe1gHMzV76e8', "kid" : b64'1Bg8vub9tLe1gHMzV76e8',
"kty" : "EC", "kty" : "EC",
"crv" : "P-256", "crv" : "P-256",
"x" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU', "x" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU',
"y" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0' "y" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0'
} }
} }
} }
Figure 19: Access Token including Public Key of the client.
Messages C and F are shown in Figure 20 - Figure 21. Figure 13: Access Token Including Public Key of the Client
C: The client then sends the PoP access token to the authz-info Messages C and F are shown in Figures 14 and 15.
endpoint at the RS. This is a plain CoAP POST request, i.e., no
transport or application-layer security is used between client and
RS since the token is integrity protected between the AS and RS.
The RS verifies that the PoP access token was created by a known
and trusted AS, that it applies to this RS, and that it is valid.
The RS caches the security context together with authorization
information about this client contained in the PoP access token.
Resource C: The client then sends the PoP access token to the authz-info
Client Server endpoint at the RS. This is a plain CoAP POST request, i.e., no
| | transport or application-layer security is used between the
C: +-------->| Header: POST (Code=0.02) client and RS since the token is integrity protected between the
| POST | Uri-Path:"authz-info" AS and RS. The RS verifies that the PoP access token was created
| | Payload: 0INDoQEKoQVN ... by a known and trusted AS, which it applies to this RS, and that
| | it is valid. The RS caches the security context together with
|<--------+ Header: 2.04 Changed authorization information about this client contained in the PoP
| 2.04 | access token.
| |
Figure 20: Access Token provisioning to RS Resource
The client and the RS runs the DTLS handshake using the raw public Client Server
keys established in step B and C. | |
The client sends a CoAP GET request to /temperature on RS over C: +-------->| Header: POST (Code=0.02)
DTLS. The RS verifies that the request is authorized, based on | POST | Uri-Path:"authz-info"
previously established security context. | | Payload: 0INDoQEKoQVN ...
F: The RS responds over the same DTLS channel with a CoAP 2.05 | |
Content response, containing a resource representation as payload. |<--------+ Header: 2.04 Changed
| 2.04 |
| |
Figure 14: Access Token Provisioning to the RS
The client and the RS runs the DTLS handshake using the raw public
keys established in steps B and C.
The client sends a CoAP GET request to /temperature on the RS over
DTLS. The RS verifies that the request is authorized based on
previously established security context.
F: The RS responds over the same DTLS channel with a CoAP 2.05
Content response containing a resource representation as payload.
Resource Resource
Client Server Client Server
| | | |
|<=======>| DTLS Connection Establishment |<=======>| DTLS Connection Establishment
| | using Raw Public Keys | | using Raw Public Keys
| | | |
+-------->| Header: GET (Code=0.01) +-------->| Header: GET (Code=0.01)
| GET | Uri-Path: "temperature" | GET | Uri-Path: "temperature"
| | | |
| | | |
| | | |
F: |<--------+ Header: 2.05 Content F: |<--------+ Header: 2.05 Content
| 2.05 | Payload: <sensor value> | 2.05 | Payload: <sensor value>
| | | |
Figure 21: Resource Request and Response protected by DTLS.
Figure 15: Resource Request and Response Protected by DTLS
F.2. Introspection Aided Token Validation F.2. Introspection Aided Token Validation
In this deployment scenario it is assumed that a client is not able In this deployment scenario, it is assumed that a client is not able
to access the AS at the time of the access request, whereas the RS is to access the AS at the time of the access request, whereas the RS is
assumed to be connected to the back-end infrastructure. Thus the RS assumed to be connected to the back-end infrastructure. Thus, the RS
can make use of token introspection. This access procedure involves can make use of token introspection. This access procedure involves
steps A-F of Figure 1, but assumes steps A and B have been carried steps (A)-(F) of Figure 1 but assumes steps (A) and (B) have been
out during a phase when the client had connectivity to AS. carried out during a phase when the client had connectivity to the
AS.
Since the client is assumed to be offline, at least for a certain Since the client is assumed to be offline, at least for a certain
period of time, a pre-provisioned access token has to be long-lived. period of time, a preprovisioned access token has to be long lived.
Since the client is constrained, the token will not be self contained Since the client is constrained, the token will not be self-contained
(i.e. not a CWT) but instead just a reference. The resource server (i.e., not a CWT) but instead just a reference. The resource server
uses its connectivity to learn about the claims associated to the uses its connectivity to learn about the claims associated to the
access token by using introspection, which is shown in the example access token by using introspection, which is shown in the example
below. below.
In the example interactions between an offline client (key fob), an In the example, interactions between an offline client (key fob), an
RS (online lock), and an AS is shown. It is assumed that there is a RS (online lock), and an AS is shown. It is assumed that there is a
provisioning step where the client has access to the AS. This provisioning step where the client has access to the AS. This
corresponds to message exchanges A and B which are shown in corresponds to message exchanges A and B, which are shown in
Figure 22. Figure 16.
Authorization consent from the resource owner can be pre-configured, Authorization consent from the resource owner can be preconfigured,
but it can also be provided via an interactive flow with the resource but it can also be provided via an interactive flow with the resource
owner. An example of this for the key fob case could be that the owner. An example of this for the key fob case could be that the
resource owner has a connected car, he buys a generic key that he resource owner has a connected car that he buys a generic key for and
wants to use with the car. To authorize the key fob he connects it wants to use with the car. To authorize the key fob, he connects it
to his computer that then provides the UI for the device. After that to his computer that then provides the UI for the device. After
OAuth 2.0 implicit flow can used to authorize the key for his car at that, OAuth 2.0 implicit flow can be used to authorize the key for
the car manufacturers AS. his car at the car manufacturers AS.
Note: In this example the client does not know the exact door it will Note: In this example, the client does not know the exact door it
be used to access since the token request is not send at the time of will be used to access since the token request is not sent at the
access. So the scope and audience parameters are set quite wide to time of access. So the scope and audience parameters are set quite
start with, while tailored values narrowing down the claims to the wide to start with, while tailored values narrowing down the claims
specific RS being accessed can be provided to that RS during an to the specific RS being accessed can be provided to that RS during
introspection step. an introspection step.
A: The client sends a CoAP POST request to the token endpoint at A: The client sends a CoAP POST request to the token endpoint at the
AS. The request contains the Audience parameter set to "PACS1337" AS. The request contains the audience parameter set to
(PACS, Physical Access System), a value the that identifies the "PACS1337" (Physical Access System (PACS)), a value that
physical access control system to which the individual doors are identifies the physical access control system to which the
connected. The AS generates an access token as an opaque string, individual doors are connected. The AS generates an access token
which it can match to the specific client and the targeted as an opaque string, which it can match to the specific client
audience. It furthermore generates a symmetric proof-of- and the targeted audience. It furthermore generates a symmetric
possession key. The communication security and authentication proof-of-possession key. The communication security and
between client and AS is assumed to have been provided at authentication between the client and AS is assumed to have been
transport layer (e.g. via DTLS) using a pre-shared security provided at the transport layer (e.g., via DTLS) using a pre-
context (psk, rpk or certificate). shared security context (pre-shared key (PSK), RPK, or
B: The AS responds with a CoAP 2.05 Content response, containing certificate).
as payload the Access Information, including the access token and
the symmetric proof-of-possession key. Communication security
between C and RS will be DTLS and PreSharedKey. The PoP key is
used as the PreSharedKey.
Note: In this example we are using a symmetric key for a multi-RS B: The AS responds with a CoAP 2.05 Content response, containing as
payload the Access Information, including the access token and
the symmetric proof-of-possession key. Communication security
between the C and RS will be DTLS and PreSharedKey. The PoP key
is used as the PreSharedKey.
Note: In this example, we are using a symmetric key for a multi-RS
audience, which is not recommended normally (see Section 6.9). audience, which is not recommended normally (see Section 6.9).
However in this case the risk is deemed to be acceptable, since all However, in this case, the risk is deemed to be acceptable, since all
the doors are part of the same physical access control system, and the doors are part of the same physical access control system;
therefore the risk of a malicious RS impersonating the client towards therefore, the risk of a malicious RS impersonating the client
another RS is low. towards another RS is low.
Authorization Authorization
Client Server Client Server
| | | |
|<=======>| DTLS Connection Establishment |<=======>| DTLS Connection Establishment
| | and mutual authentication | | and mutual authentication
| | | |
A: +-------->| Header: POST (Code=0.02) A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"token" | POST | Uri-Path:"token"
| | Content-Format: application/ace+cbor | | Content-Format: application/ace+cbor
| | Payload: <Request-Payload> | | Payload: <Request-Payload>
| | | |
B: |<--------+ Header: 2.05 Content B: |<--------+ Header: 2.05 Content
| | Content-Format: application/ace+cbor | | Content-Format: application/ace+cbor
| 2.05 | Payload: <Response-Payload> | 2.05 | Payload: <Response-Payload>
| | | |
Figure 22: Token Request and Response using Client Credentials. Figure 16: Token Request and Response Using Client Credentials
The information contained in the Request-Payload and the Response- The information contained in the Request-Payload and the Response-
Payload is shown in Figure 23. Payload is shown in Figure 17.
Request-Payload: Request-Payload:
{ {
"client_id" : "keyfob", "client_id" : "keyfob",
"audience" : "PACS1337" "audience" : "PACS1337"
} }
Response-Payload: Response-Payload:
{ {
"access_token" : b64'VGVzdCB0b2tlbg==', "access_token" : b64'VGVzdCB0b2tlbg==',
"cnf" : { "cnf" : {
"COSE_Key" : { "COSE_Key" : {
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk', "kid" : b64'c29tZSBwdWJsaWMga2V5IGlk',
"kty" : "oct", "kty" : "oct",
"alg" : "HS256", "alg" : "HS256",
"k": b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE' "k": b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE'
} }
} }
} }
Figure 23: Request and Response Payload for C offline Figure 17: Request and Response Payload for the C Offline
The access token in this case is just an opaque byte string In this case, the access token is just an opaque byte string
referencing the authorization information at the AS. referencing the authorization information at the AS.
C: Next, the client POSTs the access token to the authz-info C: Next, the client POSTs the access token to the authz-info
endpoint in the RS. This is a plain CoAP request, i.e., no DTLS endpoint in the RS. This is a plain CoAP request, i.e., no DTLS
between client and RS. Since the token is an opaque string, the between the client and RS. Since the token is an opaque string,
RS cannot verify it on its own, and thus defers to respond the the RS cannot verify it on its own, and thus defers to respond to
client with a status code until after step E. the client with a status code until after step E.
D: The RS sends the token to the introspection endpoint on the AS D: The RS sends the token to the introspection endpoint on the AS
using a CoAP POST request. In this example RS and AS are assumed using a CoAP POST request. In this example, the RS and AS are
to have performed mutual authentication using a pre shared assumed to have performed mutual authentication using a pre-
security context (psk, rpk or certificate) with the RS acting as shared security context (PSK, RPK, or certificate) with the RS
DTLS client. acting as the DTLS client.
E: The AS provides the introspection response (2.05 Content) E: The AS provides the introspection response (2.05 Content)
containing parameters about the token. This includes the containing parameters about the token. This includes the
confirmation key (cnf) parameter that allows the RS to verify the confirmation key (cnf) parameter that allows the RS to verify the
client's proof of possession in step F. Note that our example in client's proof of possession in step F. Note that our example in
Figure 25 assumes a pre-established key (e.g. one used by the Figure 19 assumes a preestablished key (e.g., one used by the
client and the RS for a previous token) that is now only client and the RS for a previous token) that is now only
referenced by its key-identifier 'kid'. referenced by its key identifier 'kid'.
After receiving message E, the RS responds to the client's POST in
step C with the CoAP response code 2.01 (Created).
Resource After receiving message E, the RS responds to the client's POST
Client Server in step C with the CoAP response code 2.01 (Created).
| |
C: +-------->| Header: POST (T=CON, Code=0.02)
| POST | Uri-Path:"authz-info"
| | Payload: b64'VGVzdCB0b2tlbg=='
| |
| | Authorization
| | Server
| | |
| D: +--------->| Header: POST (Code=0.02)
| | POST | Uri-Path: "introspect"
| | | Content-Format: "application/ace+cbor"
| | | Payload: <Request-Payload>
| | |
| E: |<---------+ Header: 2.05 Content
| | 2.05 | Content-Format: "application/ace+cbor"
| | | Payload: <Response-Payload>
| | |
| |
|<--------+ Header: 2.01 Created
| 2.01 |
| |
Figure 24: Token Introspection for C offline Resource
The information contained in the Request-Payload and the Response- Client Server
Payload is shown in Figure 25. | |
Request-Payload: C: +-------->| Header: POST (T=CON, Code=0.02)
{ | POST | Uri-Path:"authz-info"
"token" : b64'VGVzdCB0b2tlbg==', | | Payload: b64'VGVzdCB0b2tlbg=='
"client_id" : "FrontDoor", | |
} | | Authorization
| | Server
| | |
| D: +--------->| Header: POST (Code=0.02)
| | POST | Uri-Path: "introspect"
| | | Content-Format: "application/ace+cbor"
| | | Payload: <Request-Payload>
| | |
| E: |<---------+ Header: 2.05 Content
| | 2.05 | Content-Format: "application/ace+cbor"
| | | Payload: <Response-Payload>
| | |
| |
|<--------+ Header: 2.01 Created
| 2.01 |
| |
Response-Payload: Figure 18: Token Introspection for the C Offline
{
"active" : true,
"aud" : "lockOfDoor4711",
"scope" : "open, close",
"iat" : 1563454000,
"cnf" : {
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk'
}
}
Figure 25: Request and Response Payload for Introspection The information contained in the Request-Payload and the Response-
Payload is shown in Figure 19.
The client uses the symmetric PoP key to establish a DTLS Request-Payload:
PreSharedKey secure connection to the RS. The CoAP request PUT is {
sent to the uri-path /state on the RS, changing the state of the "token" : b64'VGVzdCB0b2tlbg==',
door to locked. "client_id" : "FrontDoor",
F: The RS responds with a appropriate over the secure DTLS }
channel.
Response-Payload:
{
"active" : true,
"aud" : "lockOfDoor4711",
"scope" : "open, close",
"iat" : 1563454000,
"cnf" : {
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk'
}
}
Figure 19: Request and Response Payload for Introspection
The client uses the symmetric PoP key to establish a DTLS
PreSharedKey secure connection to the RS. The CoAP request PUT is
sent to the uri-path /state on the RS, changing the state of the door
to locked.
F: The RS responds with an appropriate over the secure DTLS channel.
Resource Resource
Client Server Client Server
| | | |
|<=======>| DTLS Connection Establishment |<=======>| DTLS Connection Establishment
| | using Pre Shared Key | | using Pre Shared Key
| | | |
+-------->| Header: PUT (Code=0.03) +-------->| Header: PUT (Code=0.03)
| PUT | Uri-Path: "state" | PUT | Uri-Path: "state"
| | Payload: <new state for the lock> | | Payload: <new state for the lock>
| | | |
F: |<--------+ Header: 2.04 Changed F: |<--------+ Header: 2.04 Changed
| 2.04 | Payload: <new state for the lock> | 2.04 | Payload: <new state for the lock>
| | | |
Figure 26: Resource request and response protected by OSCORE Figure 20: Resource Request and Response Protected by OSCORE
Acknowledgments
This document is a product of the ACE Working Group of the IETF.
Thanks to Eve Maler for her contributions to the use of OAuth 2.0 and
Unlicensed Mobile Access (UMA) in IoT scenarios, Robert Taylor for
his discussion input, and Malisa Vucinic for his input on the
predecessors of this proposal.
Thanks to the authors of "[POP-KEY-DIST]OAuth 2.0
Proof-of-Possession: Authorization Server to Client Key Distribution"
[POP-KEY-DIST], from where parts of the security considerations where
copied.
Thanks to Stefanie Gerdes, Olaf Bergmann, and Carsten Bormann for
contributing their work on AS discovery from "Delegated CoAP
Authentication and Authorization Framework (DCAF)" [DCAF] (see
Section 5.1) and the considerations on multiple access tokens.
Thanks to Jim Schaad and Mike Jones for their comprehensive reviews.
Thanks to Benjamin Kaduk for his input on various questions related
to this work.
Thanks to Cigdem Sengul for some very useful review comments.
Thanks to Carsten Bormann for contributing the text for the CoRE
Resource Type registry.
Thanks to Roman Danyliw for suggesting Appendix E (including its
contents).
Ludwig Seitz and Göran Selander worked on this document as part of
the CelticPlus project CyberWI, with funding from Vinnova. Ludwig
Seitz was also received further funding for this work by Vinnova in
the context of the CelticNext project CRITISEC.
Authors' Addresses Authors' Addresses
Ludwig Seitz Ludwig Seitz
Combitech Combitech
Djäknegatan 31 Djäknegatan 31
SE-211 35 Malmö SE-211 35 Malmö
Sweden Sweden
Email: ludwig.seitz@combitech.com Email: ludwig.seitz@combitech.com
Goeran Selander Göran Selander
Ericsson Ericsson
Faroegatan 6 Faroegatan 6
SE-164 80 Kista SE-164 80 Kista
Sweden Sweden
Email: goran.selander@ericsson.com Email: goran.selander@ericsson.com
Erik Wahlstroem Erik Wahlstroem
Sweden Sweden
Email: erik@wahlstromstekniska.se Email: erik@wahlstromstekniska.se
Samuel Erdtman Samuel Erdtman
Spotify AB Spotify AB
Birger Jarlsgatan 61, 4tr Birger Jarlsgatan 61, 4tr
SE-113 56 Stockholm SE-113 56 Stockholm
Sweden Sweden
Email: erdtman@spotify.com Email: erdtman@spotify.com
Hannes Tschofenig Hannes Tschofenig
 End of changes. 551 change blocks. 
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