Updates to Audience Values for OAuth 2.0 Authorization Servers
draft-ietf-oauth-rfc7523bis-02

OAuth Working Group                                           M.B. Jones
Internet-Draft                                    Self-Issued Consulting
Updates: 7521, 7522, 7523, 9126 (if approved)                B. Campbell
Intended status: Standards Track                           Ping Identity
Expires: 23 January 2026                                    C. Mortimore
                                                                  Disney
                                                               F. Skokan
                                                                    Okta
                                                            22 July 2025

     Updates to Audience Values for OAuth 2.0 Authorization Servers
                     draft-ietf-oauth-rfc7523bis-02

Abstract

   This specification updates the requirements for audience values for
   tokens whose audience is an OAuth 2.0 authorization server to address
   a security vulnerability identified in the previous requirements for
   those audience values in multiple OAuth 2.0 specifications.

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 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
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 23 January 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components

Jones, et al.            Expires 23 January 2026                [Page 1]
Internet-Draft     Updates to Audience Values for ASs          July 2025

   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Updates to RFC 7521 . . . . . . . . . . . . . . . . . . . . .   3
   3.  Updates to RFC 7522 . . . . . . . . . . . . . . . . . . . . .   4
   4.  Updates to RFC 7523 . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Client Authentication JWT Example . . . . . . . . . . . .   8
   5.  Updates to RFC 9126 . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Media Type Registration . . . . . . . . . . . . . . . . .  10
       7.1.1.  Registry Contents . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  13
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Multiple OAuth 2.0 specifications use tokens (also known as
   "assertions") that are sent to authorization servers.  These tokens
   contain an audience value or values intended to identify the
   recipients that the token is intended for.  When the token is a JSON
   Web Token (JWT) [JWT], the audience value(s) are contained in the aud
   (audience) claim.

   When performing a security analysis of a pre-final version of the
   OpenID Federation specification [OpenID.Federation], University of
   Stuttgart security researchers Pedram Hosseyni, Dr. Ralf Küsters, and
   Tim Würtele discovered a vulnerability affecting multiple OpenID and
   OAuth specifications caused by ambiguities in the audience values of
   tokens sent to authorization servers.  The vulnerability was
   disclosed to the OAuth working group in an interim meeting in January
   2025 called for that purpose, including providing a description of
   the vulnerability [private_key_jwt.Disclosure].  A paper they
   published describing the attack is [Audience.Injection].

Jones, et al.            Expires 23 January 2026                [Page 2]
Internet-Draft     Updates to Audience Values for ASs          July 2025

   This specification updates the affected OAuth specifications to
   address the security vulnerability identified.  Specifically, it
   eliminates former ambiguities in the audience values of tokens sent
   to OAuth 2.0 authorization servers.

   A general description of the update made to each specification is for
   it to require that the issuer identifier URL of the authorization
   server, as defined in [RFC8414], be used as the sole value of the
   token audience.  Furthermore, the authorization server MUST reject
   any such token that does not contain its own issuer identifier as the
   sole audience value.  An explicit type for each affected kind of
   token, as defined in [RFC8725], is also defined to facilitate
   distinguishing between tokens produced in accordance with
   specifications published prior to these updates and those
   incorporating them.  Specific updates made to each affected
   specification follow.

1.1.  Notational Conventions

   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.

1.2.  Terminology

   All terms are as defined in the following specifications: "The OAuth
   2.0 Authorization Framework" [RFC6749], "Assertion Framework for
   OAuth 2.0 Client Authentication and Authorization Grants" [RFC7521],
   and "JSON Web Token (JWT)" [JWT].

2.  Updates to RFC 7521

   This section updates "Assertion Framework for OAuth 2.0 Client
   Authentication and Authorization Grants" [RFC7521] to tighten its
   audience requirements.

   The description of the Audience parameter in Section 5.1 of [RFC7521]
   (Assertion Metamodel) is replaced by:

Jones, et al.            Expires 23 January 2026                [Page 3]
Internet-Draft     Updates to Audience Values for ASs          July 2025

   Audience
      A value that identifies the party intended to process the
      assertion.  The audience value MUST identify the authorization
      server as the intended audience.  It is the responsibility of the
      client to use only audience values that are specific to the
      authorization server being used.  This MAY be the issuer
      identifier of the authorization server.  The authorization server
      MUST reject any assertion that does not contain its own identity
      as the intended audience.

   The description of the Audience parameter in Section 5.2 of [RFC7521]
   (General Assertion Format and Processing Rules) is replaced by:

      The assertion MUST contain an audience value that identifies the
      authorization server as the intended audience.  It is the
      responsibility of the client to use only audience values that are
      specific to the authorization server being used.  The
      authorization server MUST reject any assertion that does not
      contain its own identity as the intended audience.

3.  Updates to RFC 7522

   This section updates "Security Assertion Markup Language (SAML) 2.0
   Profile for OAuth 2.0 Client Authentication and Authorization Grants"
   [RFC7522].  It tightens its audience requirements for SAML
   authorization grants and it deprecates the use of SAML assertions for
   client authentication.

   The text and example in Section 2.2 of [RFC7522] (Using SAML
   Assertions for Client Authentication) is replaced by:

      It is RECOMMENDED that SAML Bearer Assertions not be used for for
      client authentication.

   The description of the Audience element in Item 2 of Section 3 of
   [RFC7522] (Assertion Format and Processing Requirements) is replaced
   by:

      The Assertion MUST contain a <Conditions> element with an
      <AudienceRestriction> element with an <Audience> element that
      identifies the authorization server as the intended audience.  It
      is the responsibility of the client to use only audience values
      that are specific to the authorization server being used.  This
      MAY be the issuer identifier of the authorization server, the
      token endpoint URL of the authorization server, or a SAML Entity
      ID.  Section 2.5.1.4 of "Assertions and Protocols for the OASIS
      Security Assertion Markup Language (SAML) V2.0"
      [OASIS.saml-core-2.0-os] defines the <AudienceRestriction> and

Jones, et al.            Expires 23 January 2026                [Page 4]
Internet-Draft     Updates to Audience Values for ASs          July 2025

      <Audience> elements.  The authorization server MUST reject any
      assertion that does not contain its own identity as the intended
      audience.

   In Section 4 of [RFC7522] (Authorization Grant Example), the
   sentence:

      The intended audience of the Assertion is https://saml-
      sp.example.net, which is an identifier for a SAML Service Provider
      with which the authorization server identifies itself.

   is replaced by:

      The intended audience of the Assertion is
      https://authz.example.net, which is the authorization server's
      issuer identifier.

   In the same section, the SAML 2.0 Assertion example is replaced by:

Jones, et al.            Expires 23 January 2026                [Page 5]
Internet-Draft     Updates to Audience Values for ASs          July 2025

     <Assertion IssueInstant="2025-07-17T00:53:34.619Z"
       ID="ef1xsbZxPV2oqjd7HTLRLIBlBb7"
       Version="2.0"
       xmlns="urn:oasis:names:tc:SAML:2.0:assertion">
      <Issuer>https://saml-idp.example.com</Issuer>
      <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
       [...omitted for brevity...]
      </ds:Signature>
      <Subject>
       <NameID
        Format="urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress">
        brian@example.com
       </NameID>
       <SubjectConfirmation
         Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
        <SubjectConfirmationData
          NotOnOrAfter="2025-07-17T00:58:34.619Z"
          Recipient="https://authz.example.net/token.oauth2"/>
        </SubjectConfirmation>
       </Subject>
       <Conditions>
         <AudienceRestriction>
           <Audience>https://authz.example.net</Audience>
         </AudienceRestriction>
       </Conditions>
       <AuthnStatement AuthnInstant="2025-07-17T00:53:34.371Z">
         <AuthnContext>
           <AuthnContextClassRef>
             urn:oasis:names:tc:SAML:2.0:ac:classes:X509
           </AuthnContextClassRef>
         </AuthnContext>
       </AuthnStatement>
     </Assertion>

                    Figure 1: Example SAML 2.0 Assertion

4.  Updates to RFC 7523

   This section updates "JSON Web Token (JWT) Profile for OAuth 2.0
   Client Authentication and Authorization Grants" [RFC7523] to tighten
   its audience requirements.

   In Section 2.2 of [RFC7523] (Using JWTs for Client Authentication),
   the example is replaced by:

Jones, et al.            Expires 23 January 2026                [Page 6]
Internet-Draft     Updates to Audience Values for ASs          July 2025

    POST /token.oauth2 HTTP/1.1
    Host: as.example.com
    Content-Type: application/x-www-form-urlencoded

    grant_type=authorization_code&
    code=n0esc3NRze7LTCu7iYzS6a5acc3f0ogp4&
    client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3A
      client-assertion-type%3Ajwt-bearer&
    client_assertion=eyJ0eXAiOiJjbGllbnQtYXV0aGVudGljYXRpb24rand0IiwiYWx
      nIjoiRVMyNTYiLCJraWQiOiIxNiJ9.
    e2F1ZDpodHRwczovL2F1dGh6LmV4YW1wbGUubmV0LA[...omitted...].
    cC4hiUPo[...omitted for brevity...]

   In Section 3 of [RFC7523] (JWT Format and Processing Requirements),
   Item 3, which describes the audience value, is replaced by:

      The JWT MUST contain an aud (audience) claim containing a value
      that identifies the authorization server as the intended audience.
      Two cases are differentiated:

      a.  For the authorization grant, it is the responsibility of the
          client to use only audience values that are specific to the
          authorization server being used.  This MAY be either the
          issuer identifier of the authorization server or the token
          endpoint URL of the authorization server.  The authorization
          server MUST reject any JWT that does not contain its own
          identity as the intended audience, and if the value of aud is
          an array, all array values MUST identify the authorization
          server as the intended audience.

      b.  For client authentication, the aud (audience) claim value MUST
          use the issuer identifier [RFC8414] of the authorization
          server as its sole value.  The authorization server MUST have
          an issuer identifier to be used with this specification.
          Unlike the aud value specified in [RFC7523], there MUST be no
          value other than the issuer identifier of the intended
          authorization server used as the audience of the JWT; this
          includes that the token endpoint URL of the authorization
          server MUST NOT be used as an audience value.  To simplify
          implementations, the aud claim value MUST be a JSON string,
          and not a single-valued JSON array.  The authorization server
          MUST reject any JWT that does not contain its issuer
          identifier as its sole audience value.

      In the absence of an application profile specifying otherwise,
      applications MUST compare the audience values using the Simple
      String Comparison method defined in Section 6.2.1 of RFC 3986
      [RFC3986].

Jones, et al.            Expires 23 January 2026                [Page 7]
Internet-Draft     Updates to Audience Values for ASs          July 2025

   In Section 3.2 of [RFC7523] (Client Authentication Processing), the
   following requirement is added:

      Client authentication JWTs MUST be explicitly typed by using the
      typ header parameter value client-authentication+jwt another more
      specific explicit type value defined by a specification profiling
      this specification.  Client authentication JWTs not using the
      explicit type value MUST be rejected by the authorization server.

   In Section 4 of [RFC7523] (Authorization Grant Example), the
   sentence:

      The intended audience of the JWT is https://jwt-rp.example.net,
      which is an identifier with which the authorization server
      identifies itself.

   is replaced by:

      The intended audience of the JWT is https://authz.example.net,
      which is the authorization server's issuer identifier.

   In the same section, the JWT Claims Set example is replaced by:

     {"aud":"https://authz.example.net",
      "iss":"https://jwt-idp.example.com",
      "sub":"mailto:mike@example.com",
      "iat":1731721541,
      "exp":1731725141,
      "http://claims.example.com/member":true
     }

                      Figure 2: Example JWT Claims Set

   In the list of agreements required by participants in Section 5 of
   [RFC7523] (Interoperability Considerations), an agreement on
   "audience identifiers" is no longer needed for client authentication
   JWTs.

   The additional example in the following subsection is added after
   Section 4 of [RFC7523]

4.1.  Client Authentication JWT Example

   The following example illustrates what a client authentication JWT
   and token request using it would look like.

Jones, et al.            Expires 23 January 2026                [Page 8]
Internet-Draft     Updates to Audience Values for ASs          July 2025

   The example shows a JWT issued and signed by the system entity
   identified as https://jwt-idp.example.com.  The subject of the JWT is
   identified by email address as mike@example.com.  The intended
   audience of the JWT is https://authz.example.net, which is the
   authorization server's issuer identifier.  The JWT is sent as part of
   a token request to the authorization server's token endpoint at
   https://authz.example.net/token.oauth2.

   Below is an example JSON object that could be encoded to produce the
   JWT Claims Set for a client authentication JWT:

     {"aud":"https://authz.example.net",
      "iss":"https://jwt-idp.example.com",
      "sub":"mailto:mike@example.com",
      "iat":1752702206,
      "exp":1752705806,
      "http://claims.example.com/member":true
     }

   The following example JSON object, used as the header parameters of a
   JWT, declares that the JWT is a client authentication JWT, is signed
   with the Elliptic Curve Digital Signature Algorithm (ECDSA) P-256
   with SHA-256, and was signed with a key identified by the kid value
   16.

     {"typ":"client-authentication+jwt","alg":"ES256","kid":"16"}

   To present the JWT with the claims and header parameters shown above
   as part of an access token request, for example, the client might
   make the following HTTPS request (with extra line breaks for display
   purposes only):

    POST /token.oauth2 HTTP/1.1
    Host: authz.example.net
    Content-Type: application/x-www-form-urlencoded

    grant_type=authorization_code&
    code=n0esc3NRze7LTCu7iYzS6a5acc3f0ogp4&
    client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3A
      client-assertion-type%3Ajwt-bearer&
    client_assertion=eyJ0eXAiOiJjbGllbnQtYXV0aGVudGljYXRpb24rand0IiwiYWx
      nIjoiRVMyNTYiLCJraWQiOiIxNiJ9.
    e2F1ZDpodHRwczovL2F1dGh6LmV4YW1wbGUubmV0LA[...omitted...].
    J9l-ZhwP[...omitted for brevity...]

Jones, et al.            Expires 23 January 2026                [Page 9]
Internet-Draft     Updates to Audience Values for ASs          July 2025

5.  Updates to RFC 9126

   This section updates "OAuth 2.0 Pushed Authorization Requests"
   [RFC9126] to tighten its audience requirements.

   The paragraph describing the audience value in Section 2 of [RFC9126]
   (Pushed Authorization Request Endpoint) is replaced by:

      This update resolves the potential ambiguity regarding the
      appropriate audience value to use when employing JWT client
      assertion-based authentication (as defined in Section 2.2 of
      [RFC7523] and as updated by Section 4 with the private_key_jwt or
      client_secret_jwt authentication method names per Section 9 of
      [OpenID.Core]) that was described in [RFC9126].  To address that
      ambiguity, the issuer identifier URL of the authorization server
      according to [RFC8414] MUST be used as the sole value of the
      audience.  The authorization server MUST reject any such JWT that
      does not contain its own issuer identifier as the sole audience
      value.

6.  Security Considerations

   The security considerations described within the following
   specifications are all applicable to this document: "Assertion
   Framework for OAuth 2.0 Client Authentication and Authorization
   Grants" [RFC7521], "Security Assertion Markup Language (SAML) 2.0
   Profile for OAuth 2.0 Client Authentication and Authorization Grants"
   [RFC7522], "JSON Web Token (JWT) Profile for OAuth 2.0 Client
   Authentication and Authorization Grants" [RFC7523], "OAuth 2.0 Pushed
   Authorization Requests" [RFC9126], "The OAuth 2.0 Authorization
   Framework" [RFC6749], and "JSON Web Token (JWT)" [JWT].

   This specification tightens token audience requirements to prevent
   attacks that could result from exploiting audience ambiguities
   previously allowed by [RFC7521], [RFC7522], [RFC7523], and [RFC9126].
   These attacks are described in [private_key_jwt.Disclosure] and
   [Audience.Injection].

7.  IANA Considerations

7.1.  Media Type Registration

   This section registers the following media type [RFC2046] in the
   "Media Types" registry [IANA.MediaTypes] in the manner described in
   [RFC6838].

Jones, et al.            Expires 23 January 2026               [Page 10]
Internet-Draft     Updates to Audience Values for ASs          July 2025

7.1.1.  Registry Contents

   *  Type name: application
   *  Subtype name: client-authentication+jwt
   *  Required parameters: n/a
   *  Optional parameters: n/a
   *  Encoding considerations: binary; A client authentication JWT is a
      JWT; JWT values are encoded as a series of base64url-encoded
      values (some of which may be the empty string) separated by period
      ('.') characters.
   *  Security considerations: See Section 6 of this specification
   *  Interoperability considerations: n/a
   *  Published specification: Section 4 of this specification
   *  Applications that use this media type: Applications that use this
      specification
   *  Fragment identifier considerations: n/a
   *  Additional information:
         Magic number(s): n/a
         File extension(s): n/a
         Macintosh file type code(s): n/a
   *  Person & email address to contact for further information:
      Michael B.  Jones, michael_b_jones@hotmail.com
   *  Intended usage: COMMON
   *  Restrictions on usage: none
   *  Author: Michael B.  Jones, michael_b_jones@hotmail.com
   *  Change controller: IETF
   *  Provisional registration?  No

8.  References

8.1.  Normative References

   [JWT]      Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [OASIS.saml-core-2.0-os]
              Cantor, S., Kemp, J., Philpott, R., and E. Maler,
              "Assertions and Protocols for the OASIS Security Assertion
              Markup Language (SAML) V2.0", OASIS Standard saml-core-
              2.0-os, March 2005, <https://docs.oasis-
              open.org/security/saml/v2.0/saml-core-2.0-os.pdf>.

   [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>.

Jones, et al.            Expires 23 January 2026               [Page 11]
Internet-Draft     Updates to Audience Values for ASs          July 2025

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [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>.

   [RFC7521]  Campbell, B., Mortimore, C., Jones, M., and Y. Goland,
              "Assertion Framework for OAuth 2.0 Client Authentication
              and Authorization Grants", RFC 7521, DOI 10.17487/RFC7521,
              May 2015, <https://www.rfc-editor.org/info/rfc7521>.

   [RFC7522]  Campbell, B., Mortimore, C., and M. Jones, "Security
              Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0
              Client Authentication and Authorization Grants", RFC 7522,
              DOI 10.17487/RFC7522, May 2015,
              <https://www.rfc-editor.org/info/rfc7522>.

   [RFC7523]  Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token
              (JWT) Profile for OAuth 2.0 Client Authentication and
              Authorization Grants", RFC 7523, DOI 10.17487/RFC7523, May
              2015, <https://www.rfc-editor.org/info/rfc7523>.

   [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>.

   [RFC8414]  Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
              Authorization Server Metadata", RFC 8414,
              DOI 10.17487/RFC8414, June 2018,
              <https://www.rfc-editor.org/info/rfc8414>.

   [RFC8725]  Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
              Current Practices", BCP 225, RFC 8725,
              DOI 10.17487/RFC8725, February 2020,
              <https://www.rfc-editor.org/info/rfc8725>.

   [RFC9126]  Lodderstedt, T., Campbell, B., Sakimura, N., Tonge, D.,
              and F. Skokan, "OAuth 2.0 Pushed Authorization Requests",
              RFC 9126, DOI 10.17487/RFC9126, September 2021,
              <https://www.rfc-editor.org/info/rfc9126>.

8.2.  Informative References

Jones, et al.            Expires 23 January 2026               [Page 12]
Internet-Draft     Updates to Audience Values for ASs          July 2025

   [Audience.Injection]
              Hosseyni, P., Küsters, R., and T. Würtele, "Audience
              Injection Attacks: A New Class of Attacks on Web-Based
              Authorization and Authentication Standards", Cryptology
              ePrint Archive Paper 2025/629, April 2025,
              <https://eprint.iacr.org/2025/629>.

   [IANA.MediaTypes]
              IANA, "Media Types",
              <https://www.iana.org/assignments/media-types>.

   [OpenID.Core]
              Sakimura, N., Bradley, J., Jones, M.B., de Medeiros, B.,
              and C. Mortimore, "OpenID Connect Core 1.0 incorporating
              errata set 2", 15 December 2023,
              <https://openid.net/specs/openid-connect-core-1_0.html>.

   [OpenID.Federation]
              Hedberg, R., Jones, M. B., Solberg, A., Bradley, J.,
              Marco, G. D., and V. Dzhuvinov, "OpenID Federation 1.0", 2
              June 2025,
              <https://openid.net/specs/openid-federation-1_0.html>.

   [private_key_jwt.Disclosure]
              OpenID Foundation, "OIDF Responsible Disclosure Notice on
              Security Vulnerability for private_key_jwt", 24 January
              2025, <https://openid.net/wp-content/uploads/2025/01/OIDF-
              Responsible-Disclosure-Notice-on-Security-Vulnerability-
              for-private_key_jwt.pdf>.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <https://www.rfc-editor.org/info/rfc2046>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

Appendix A.  Document History

   [[ to be removed by the RFC Editor before publication as an RFC ]]

   -02

   *  Added Filip Skokan as an author.

Jones, et al.            Expires 23 January 2026               [Page 13]
Internet-Draft     Updates to Audience Values for ASs          July 2025

   *  Applied Brian Campbell's suggestions made at IETF 122.
      Specifically:

      -  Focused RFC 7523 updates on JWT client authentication case.

      -  Described client responsibilities for the audience value of
         authorization grants.  No longer mandate that the audience for
         authorization grants be the issuer identifier, so as to make a
         minimum of breaking changes.

      -  Deprecated the use of SAML assertions for client
         authentication.

   -01

   *  Reworked to make updates to RFC 7523, rather than replacing it.

   *  Removed updates to RFC 9101.

   *  Added reference to the University of Stuttgart paper
      [Audience.Injection].

   -00

   *  Initial working group draft, replacing draft-jones-oauth-
      rfc7523bis-00.

Acknowledgements

   We would like to acknowledge the contributions of the following
   people to this specification: John Bradley, Ralph Bragg, Joseph
   Heenan, Pedram Hosseyni, Aaron Parecki, and Tim Würtele.

Authors' Addresses

   Michael B. Jones
   Self-Issued Consulting
   Email: michael_b_jones@hotmail.com
   URI:   https://self-issued.info/

   Brian Campbell
   Ping Identity
   Email: bcampbell@pingidentity.com

   Chuck Mortimore
   Disney

Jones, et al.            Expires 23 January 2026               [Page 14]
Internet-Draft     Updates to Audience Values for ASs          July 2025

   Email: charliemortimore@gmail.com

   Filip Skokan
   Okta
   Email: panva.ip@gmail.com

Jones, et al.            Expires 23 January 2026               [Page 15]