ACE Working Group

Internet Engineering Task Force (IETF)                          L. Seitz
Internet-Draft
Request for Comments: 9201                                     Combitech
Intended status:
Category: Standards Track                             May 5, 2021
Expires: November 6, 2021                                     March 2022
ISSN: 2070-1721

  Additional OAuth Parameters for Authentication and Authorization in for
                     Constrained Environments (ACE)
                     draft-ietf-ace-oauth-params-15

Abstract

   This specification defines new parameters and encodings for the OAuth
   2.0 token and introspection endpoints when used with the framework
   for authentication Authentication and authorization Authorization for constrained environments Constrained Environments
   (ACE).  These are used to express the proof-of-possession key the
   client wishes to use, the proof-of-possession key that the
   Authorization Server
   authorization server has selected, and the proof-of-possession key
   the Resource Server resource server uses to authenticate to the client.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list  It represents the consensus of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid the IETF community.  It has
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   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of six months this document, any errata,
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   This Internet-Draft will expire on November 6, 2021.
   https://www.rfc-editor.org/info/rfc9201.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Parameters for the Token Endpoint . . . . . . . . . . . . . .   3
     3.1.  Client-to-AS Request  . . . . . . . . . . . . . . . . . .   3
     3.2.  AS-to-Client Response . . . . . . . . . . . . . . . . . .   4
   4.  Parameters for the Introspection Endpoint . . . . . . . . . .   6
   5.  Confirmation Method Parameters  . . . . . . . . . . . . . . .   7
   6.  CBOR Mappings . . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Requirements when using asymmetric keys . . . . . . . . . . .   8 When Using Asymmetric Keys
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  OAuth Parameter Registration . . . . . . . . . . . . . .   9
     10.2.  OAuth Parameters CBOR Mappings Registration  . . . . . .   9
     10.3.  OAuth Token Introspection Response CBOR Mappings
            Registration . . . . . . . . . . . . . . . . . . . . . .  10
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     12.1.
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     12.2.
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Acknowledgments
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The Authentication and Authorization for Constrained Environments
   (ACE) specification [I-D.ietf-ace-oauth-authz] [RFC9200] requires some new parameters for
   interactions with the OAuth 2.0 [RFC6749] token and introspection
   endpoints, as well as some new claims to be used in access tokens.
   These parameters and claims can also be used in other contexts and
   have therefore been put into a dedicated document, document to facilitate their
   use in a manner independent of
   [I-D.ietf-ace-oauth-authz]. [RFC9200].

   Note that although all examples are shown in Concise Binary Object
   Representation (CBOR) [RFC8949], JSON [RFC8259] MAY be used as an
   alternative for HTTP-based communications, as specified in
   [I-D.ietf-ace-oauth-authz]. [RFC9200].

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Readers are assumed to be familiar with the terminology from
   [I-D.ietf-ace-oauth-authz],
   [RFC9200], especially the terminology for entities in the
   architecture such as client (C), resource server (RS) (RS), and
   authorization server (AS).

   Terminology from [RFC8152] is used in the examples, especially
   COSE_Key
   COSE_Key, which is defined in section Section 7 of [RFC8152].

   Note that the term "endpoint" is used here following its OAuth 2.0
   [RFC6749] definition, which is to denote resources such as token and
   introspection at the AS and authz-info at the RS.  The Constrained
   Application Protocol (CoAP) [RFC7252] definition, which is "An "[a]n
   entity participating in the CoAP protocol" protocol", is not used in this
   specification.

3.  Parameters for the Token Endpoint

   This section defines additional parameters for the interactions with
   the token endpoint in the ACE framework [I-D.ietf-ace-oauth-authz]. [RFC9200].

3.1.  Client-to-AS Request

   This section defines the "req_cnf" parameter allowing clients to
   request a specific proof-of-possession key in an access token from a
   token endpoint in the ACE framework [I-D.ietf-ace-oauth-authz]: [RFC9200]:

   req_cnf
      OPTIONAL.  This field contains information about the key the
      client would like to bind to the access token for proof-of- proof of
      possession.  It is RECOMMENDED that an AS rejects a request
      containing a symmetric key value in the 'req_cnf' "req_cnf" field
      (kty=Symmetric), since the AS is expected to be able to generate
      better symmetric keys than a constrained client client.  (Note: this does
      not apply to key identifiers referencing a symmetric key). key.)  The AS
      MUST verify that the client really is in possession of the
      corresponding key.  Profiles of [I-D.ietf-ace-oauth-authz] [RFC9200] using this specification
      MUST define the proof-of-possession method used by the AS, AS if they
      allow clients to use this request parameter.  Values of this
      parameter follow the syntax and semantics of the "cnf" claim
      either from section Section 3.1 of [RFC8747] for CBOR-based interactions
      or from section Section 3.1 of [RFC7800] for JSON-based interactions.

   Figure 1 shows a request for an access token using the "req_cnf"
   parameter to request a specific public key as a proof-of-possession
   key.  The content is displayed in CBOR diagnostic notation, notation without
   abbreviations and with line-breaks line breaks for better readability.

   Header: POST (Code=0.02)
   Uri-Host: "as.example.com"
   Uri-Path: "token"
   Content-Format: "application/ace+cbor"
   Payload:
   {
      "req_cnf" : {
         "COSE_Key" : {
            "kty" : "EC2",
            "kid" : h'11',
            "crv" : "P-256",
            "x" : h'BAC5B11CAD8F99F9C72B05CF4B9E26D24
                    4DC189F745228255A219A86D6A09EFF',
            "y" : h'20138BF82DC1B6D562BE0FA54AB7804A3
                    A64B6D72CCFED6B6FB6ED28BBFC117E'
         }
      }
    }

         Figure 1: Example request Request for an access token bound Access Token Bound to an asymmetric
                                   key.
                               Asymmetric Key

3.2.  AS-to-Client Response

   This section defines the following additional parameters for an AS
   response to a request to the token endpoint:

   cnf
      REQUIRED if the token type is "pop" and a symmetric key is used.
      MAY be present for asymmetric proof-of-possession keys.  This
      field contains the proof-of-possession key that the AS selected
      for the token.  Values of this parameter follow the syntax and
      semantics of the "cnf" claim either from section Section 3.1 of [RFC8747]
      for CBOR-based interactions or from section Section 3.1 of [RFC7800] for
      JSON-based interactions.  See Section 5 for additional discussion
      of the usage of this parameter.

   rs_cnf
      OPTIONAL if the token type is "pop" and asymmetric keys are used.
      MUST NOT be present otherwise.  This field contains information
      about the public key used by the RS to authenticate.  If this
      parameter is absent, either the RS does not use a public key or
      the AS knows that the RS can authenticate itself to the client
      without additional information.  Values of this parameter follow
      the syntax and semantics of the "cnf" claim either from section
      Section 3.1 of [RFC8747] for CBOR-based interactions or from section
      Section 3.1 of [RFC7800] for JSON-based interactions.  See
      Section 5 for additional discussion of the usage of this
      parameter.

   Figure 2 shows an AS response containing a token and a "cnf"
   parameter with a symmetric proof-of-possession key.

   Header: Created (Code=2.01)
   Content-Format: "application/ace+cbor"
   Payload:
   {
     "access_token" : h'4A5015DF686428 ...
      (remainder of CWT omitted for brevity;
      CWT contains COSE_Key in the "cnf" claim)',
     "cnf" : {
       "COSE_Key" : {
         "kty" : "Symmetric",
         "kid" : h'DFD1AA97',
         "k" : h'849B5786457C1491BE3A76DCEA6C427108'
       }
     }
   }

       Figure 2: Example AS response Response with an access token bound Access Token Bound to a
                              symmetric key.
                               Symmetric Key

   Figure 3 shows an AS response containing a token bound to a
   previously requested asymmetric proof-of-possession key (not shown)
   and a an "rs_cnf" parameter containing the public key of the RS.

   Header: Created (Code=2.01)
   Content-Format: "application/ace+cbor"
   Payload:
   {
     "access_token" : h'D08343A1010AA1054D2A45DF6FBC5A5A ...
      (remainder of CWT omitted for brevity)',
     "rs_cnf" : {
       "COSE_Key" : {
         "kty" : "EC2",
         "kid" : h'12',
         "crv" : "P-256",
         "x" : h'BCEE7EAAC162F91E6F330F5771211E220
                 B8B546C96589B0AC4AD0FD24C77E1F1',
         "y" : h'C647B38C55EFBBC4E62E651720F002D5D
                 75B2E0C02CD1326E662BCA222B90416'
       }
     }
   }

        Figure 3: Example AS response, including Response Including the RS's public key. Public Key

4.  Parameters for the Introspection Endpoint

   This section defines the use of CBOR instead of JSON for the "cnf"
   introspection response parameter specified in section Section 9.4 of
   [RFC8705].

   If CBOR is used instead of JSON in an interaction with the
   introspection endpoint, the AS MUST use the parameter mapping
   specified in Figure 5 Table 1 and the value must follow the syntax of "cnf"
   claim values from section Section 3.1 of [RFC8747].

   Figure 4 shows an AS response to an introspection request including
   the "cnf" parameter to indicate the proof-of-possession key bound to
   the token.

   Header: Created (Code=2.01)
   Content-Format: "application/ace+cbor"
   Payload:
   {
     "active" : true,
     "scope" : "read",
     "aud" : "tempSensor4711",
     "cnf" : {
       "COSE_Key" : {
         "kty" : "EC2",
         "kid" : h'11',
         "crv" : "P-256",
         "x" : h'BAC5B11CAD8F99F9C72B05CF4B9E26D24
                 4DC189F745228255A219A86D6A09EFF',
         "y" : h'20138BF82DC1B6D562BE0FA54AB7804A3
                 A64B6D72CCFED6B6FB6ED28BBFC117E'
       }
     }
   }

                  Figure 4: Example introspection response. Introspection Response

5.  Confirmation Method Parameters

   The confirmation method parameters are used in
   [I-D.ietf-ace-oauth-authz] [RFC9200] as follows:

   o

   *  "req_cnf" in the access token request C -> AS, OPTIONAL to
      indicate the client's raw public key, key or the key-identifier key identifier of a
      previously established key between the C and RS that the client
      wishes to use for proof-of-possession proof of possession of the access token.

   o

   *  "cnf" in the token response AS -> C, OPTIONAL if using an
      asymmetric key or a key that the client requested via a key
      identifier in the request.  REQUIRED if the client didn't specify
      a "req_cnf" and symmetric keys are used.  Used to indicate the
      symmetric key generated by the AS for proof-of-possession proof of possession of the
      access token.

   o

   *  "cnf" in the introspection response AS -> RS, REQUIRED if the
      access token that was subject to introspection is a proof-of-
      possession token, absent otherwise.  Indicates the proof-of-
      possession key bound to the access token.

   o

   *  "rs_cnf" in the token response AS -> C, OPTIONAL to indicate the
      public key of the RS, RS if it uses one to authenticate itself to the
      client and the binding between the key and RS identity is not
      established through other means.

   Note that the COSE_Key structure in a confirmation claim or parameter
   may contain an "alg" or "key_ops" parameter.  If such parameters are
   present, a client MUST NOT use a key that is incompatible with the
   profile or proof-of-possession algorithm according to those
   parameters.  An RS MUST reject a proof-of-possession proof of possession using such a key
   with a response code equivalent to the CoAP code 4.00 (Bad Request).

   If an access token is issued for an audience that includes several
   RS,
   RSs, the "rs_cnf" parameter MUST NOT be used, since the client cannot
   determine for which RS the key applies.  This document recommends to
   specify a different endpoint that the client can use to acquire RS
   authentication keys in such cases.  The specification of such an
   endpoint is out of scope for this document.

6.  CBOR Mappings

   If CBOR is used, the new parameters and claims defined in this
   document MUST be mapped to CBOR types types, as specified in Figure 5, Table 1, using
   the given integer abbreviation for the map key.

       /----------+----------+-------------------------------------\

   +=========+==========+============+========================+
   | Name    | CBOR Key | Value Type | Usage                  |
       |----------+----------+-------------------------------------|
   +=========+==========+============+========================+
   | req_cnf | TBD (4) 4        | map        | token request          |
   +---------+----------+------------+------------------------+
   | cnf     | TBD (8) 8        | map        | token response         |
   +---------+----------+------------+------------------------+
   | cnf     | TBD (8) 8        | map        | introspection response |
   +---------+----------+------------+------------------------+
   | rs_cnf  | TBD (41) 41       | map        | token response         |
       \----------+----------+------------+------------------------/

          Figure 5:
   +---------+----------+------------+------------------------+

       Table 1: CBOR mappings Mappings for new parameters New Parameters and claims. Claims

7.  Requirements when using asymmetric keys When Using Asymmetric Keys

   An RS using asymmetric keys to authenticate to the client MUST NOT
   hold several different asymmetric key pairs, pairs applicable to the same
   authentication algorithm.  For example example, when using DTLS, the RS MUST
   NOT hold several asymmetric key pairs applicable to the same cipher
   suite.  The reason for this restriction is that the RS has no way of
   determining which key to use before the client's identity is
   established.  Therefore  Therefore, authentication attempts by the RS could
   randomly fail based on which key the RS selects, unless the algorithm
   negotiation produces a unique choice of key pair for the RS.

8.  Security Considerations

   This document is an extension to [I-D.ietf-ace-oauth-authz]. [RFC9200].  All security
   considerations from that document apply here as well.

9.  Privacy Considerations

   This document is an extension to [I-D.ietf-ace-oauth-authz]. [RFC9200].  All privacy
   considerations from that document apply here as well.

10.  IANA Considerations

10.1.  OAuth Parameter Registration

   This section registers the following parameters in the "OAuth
   Parameters" registry [IANA.OAuthParameters]:

   o

   Name: "req_cnf"
   o  req_cnf
   Parameter Usage Location:  token request
   o
   Change Controller: IESG
   o  IETF
   Reference:  Section 5 of [this document]

   o RFC 9201

   Name: "rs_cnf"
   o  rs_cnf
   Parameter Usage Location:  token response
   o
   Change Controller: IESG
   o  IETF
   Reference:  Section 5 of [this document]

   o RFC 9201

   Name: "cnf"
   o  cnf
   Parameter Usage Location:  token response
   o
   Change Controller: IESG
   o  IETF
   Reference:  Section 5 of [this document] RFC 9201

10.2.  OAuth Parameters CBOR Mappings Registration

   This section registers the following parameter mappings in the "OAuth
   Parameters CBOR Mappings" registry established in section 8.9. Section 8.10 of
   [I-D.ietf-ace-oauth-authz].

   o
   [RFC9200].

   Name: "req_cnf"
   o  req_cnf
   CBOR key: TBD (suggested: 4)
   o  Change Controller: IESG
   o Key:  4
   Value Type:  map
   Reference:  Section 3.1 of [this document]

   o RFC 9201
   Original specification:  RFC 9201

   Name: "cnf"
   o  cnf
   CBOR key: TBD (suggested: 8)
   o  Change Controller: IESG
   o Key:  8
   Value Type:  map
   Reference:  Section 3.2 of [this document]

   o RFC 9201
   Original specification:  RFC 9201

   Name: "rs_cnf"
   o  rs_cnf
   CBOR key: TBD (suggested: 41)
   o  Change Controller: IESG
   o Key:  41
   Value Type:  map
   Reference:  Section 3.2 of [this document] RFC 9201
   Original specification:  RFC 9201

10.3.  OAuth Token Introspection Response CBOR Mappings Registration

   This section registers the following parameter mapping in the "OAuth
   Token Introspection Response CBOR Mappings" registry established in
   section 8.11.
   Section 8.12 of [I-D.ietf-ace-oauth-authz].

   o [RFC9200].

   Name: "cnf"
   o  cnf
   CBOR key: TBD (suggested: 8)
   o  Change Controller: IESG
   o Key:  8
   Value Type:  map
   Reference:  Section 4 of [this document] RFC 9201
   Original specification:  [RFC8705]

11.  Acknowledgments

   This document is a product of the ACE working group of the IETF.
   Special thanks to Brian Campbell for his thorough review of this
   document.

   Ludwig Seitz worked on this document as part of the CelticNext
   projects CyberWI, and CRITISEC with funding from Vinnova.

12.  References

12.1.

11.1.  Normative References

   [I-D.ietf-ace-oauth-authz]
              Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
              H. Tschofenig, "Authentication and Authorization for
              Constrained Environments (ACE) using the OAuth 2.0
              Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-40
              (work in progress), April 2021.

   [IANA.OAuthParameters]
              IANA, "OAuth Parameters",
              <https://www.iana.org/assignments/oauth-parameters/oauth-
              parameters.xhtml#parameters>.
              <https://www.iana.org/assignments/oauth-parameters>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/info/rfc6749>.

   [RFC7800]  Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
              Possession Key Semantics for JSON Web Tokens (JWTs)",
              RFC 7800, DOI 10.17487/RFC7800, April 2016,
              <https://www.rfc-editor.org/info/rfc7800>.

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8705]  Campbell, B., Bradley, J., Sakimura, N., and T.
              Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
              and Certificate-Bound Access Tokens", RFC 8705,
              DOI 10.17487/RFC8705, February 2020,
              <https://www.rfc-editor.org/info/rfc8705>.

   [RFC8747]  Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
              Tschofenig, "Proof-of-Possession Key Semantics for CBOR
              Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
              2020, <https://www.rfc-editor.org/info/rfc8747>.

   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,
              <https://www.rfc-editor.org/info/rfc8949>.

12.2.

   [RFC9200]  Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
              H. Tschofenig, "Authentication and Authorization for
              Constrained Environments (ACE) Using the OAuth 2.0
              Framework (ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200,
              March 2022, <https://www.rfc-editor.org/info/rfc9200>.

11.2.  Informative References

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

Acknowledgments

   This document is a product of the ACE Working Group of the IETF.
   Special thanks to Brian Campbell for his thorough review of this
   document.

   Ludwig Seitz worked on this document as part of the CelticNext
   projects CyberWI and CRITISEC with funding from Vinnova.

Author's Address

   Ludwig Seitz
   Combitech
   Djaeknegatan
   Djäknegatan 31
   Malmoe  211
   SE-211 35 Malmö
   Sweden
   Email: ludwig.seitz@combitech.com