JWT Response for OAuth Token Introspection
draft-ietf-oauth-jwt-introspection-response-08

Open Authentication Protocol                         T. Lodderstedt, Ed.
Internet-Draft                                                yes.com AG
Intended status: Standards Track                            V. Dzhuvinov
Expires: March 22, 2020                                  Connect2id Ltd.
                                                            Sep 19, 2019

               JWT Response for OAuth Token Introspection
             draft-ietf-oauth-jwt-introspection-response-08

Abstract

   This specification proposes an additional JSON Web Token (JWT)
   secured response for OAuth 2.0 Token Introspection.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 22, 2020.

Copyright Notice

   Copyright (c) 2019 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
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   (https://trustee.ietf.org/license-info) in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Notation and Conventions . . . . . . . . . . . .   3
   3.  Resource server management  . . . . . . . . . . . . . . . . .   3
   4.  Requesting a JWT Response . . . . . . . . . . . . . . . . . .   4
   5.  JWT Response  . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Client Metadata . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Authorization Server Metadata . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     8.1.  Cross-JWT Confusion . . . . . . . . . . . . . . . . . . .   9
     8.2.  Token Data Leakage  . . . . . . . . . . . . . . . . . . .   9
     8.3.  Keeping Token Data Confidential from OAuth Clients  . . .  10
     8.4.  Logging and Audit of Introspection Activity . . . . . . .  10
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  10
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     11.1.  OAuth Dynamic Client Registration Metadata Registration   11
       11.1.1.  Registry Contents  . . . . . . . . . . . . . . . . .  11
     11.2.  OAuth Authorization Server Metadata Registration . . . .  12
       11.2.1.  Registry Contents  . . . . . . . . . . . . . . . . .  12
     11.3.  Media Type Registration  . . . . . . . . . . . . . . . .  12
       11.3.1.  Registry Contents  . . . . . . . . . . . . . . . . .  13
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     12.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   OAuth 2.0 Token Introspection [RFC7662] specifies a method for a
   protected resource to query an OAuth 2.0 authorization server to
   determine the state of an access token and obtain data associated
   with the access token.  This enables deployments to implement opaque
   access tokens in an interoperable way.

   The introspection response, as specified in OAuth 2.0 Token
   Introspection [RFC7662], is a plain JSON object.  However, there are
   use cases where the resource server requires stronger assurance that
   the authorization server issued the token introspection response for
   an access token, including cases where the authorization server
   assumes liability for the content of the token introspection
   response.  An example is a resource server using verified person data
   to create certificates, which in turn are used to create qualified
   electronic signatures.

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   In such use cases it may be useful or even required to return a
   signed JWT [RFC7519] as the introspection response.  This
   specification extends the token introspection endpoint with the
   capability to return responses as JWTs.

2.  Requirements Notation and 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.

3.  Resource server management

   The authorization server (AS) and the resource server (RS) maintain a
   strong two-way trust relationship.  The resource server relies on the
   authorization server to obtain authorization, user and other data as
   input to its access control decisions and service delivery.  The
   authorization server relies on the resource server to handle the
   provided data appropriately.

   In the context of this specification, the Token Introspection
   Endpoint is used to convey such security data and potentially also
   privacy sensitive data related to an access token.

   In order to process the introspection requests in a secure and
   privacy-preserving manner, the authorization server MUST be able to
   identify, authenticate and authorize resource servers.

   To support encrypted token introspection response JWTs, the
   authorization server MUST also be provided with the respective
   resource server encryption keys and algorithms.

   The authorization server MUST be able to determine whether an RS is
   the audience for a particular access token and what data it is
   entitled to receive, otherwise the RS is not authorized to obtain
   data for the access token.  The AS has the discretion how to fulfil
   this requirement.  The AS could, for example, maintain a mapping
   between scopes values and resource servers.

   The requirements given above imply that the authorization server
   maintains credentials and other configuration data for each RS.

   One way is by utilizing dynamic client registration [RFC7591] and
   treating every RS as an OAuth client.  In this case, the
   authorization server is assumed to at least maintain "client_id" and
   "token_endpoint_auth_method" with complementary authentication method

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   metadata, such as "jwks" or "client_secret".  In cases where the AS
   needs to acquire consent to transmit data to a RS, the following
   client metadata fields are recommended: "client_name", "client_uri",
   "contacts", "tos_uri", "policy_uri".

   The AS MUST restrict the use of client credentials by a RS to the
   calls it requires, e.g. the AS MAY restrict such a client to call the
   token introspection endpoint only.  How the AS implements this
   restriction is beyond the scope of this specification.

   This specification further introduces client metadata to manage the
   configuration options required to sign and encrypt token
   introspection response JWTs.

4.  Requesting a JWT Response

   A resource server requests to receive a JWT introspection response by
   including an Accept header with content type "application/jwt" in the
   introspection request.

   Authentication at the token introspection endpoint can utilize client
   authentication methods or a separate access token issued to the
   resource server.  Whether a resource server is required to
   authenticate is determined by the respective RS-specific policy at
   the AS.

   The following is a non-normative example request using client
   authentication:

   POST /introspect HTTP/1.1
   Host: server.example.com
   Accept: application/jwt
   Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
   Content-Type: application/x-www-form-urlencoded

   token=2YotnFZFEjr1zCsicMWpAA

   If required by its policy, the authorization server MUST authenticate
   the caller and check its authorization to use the token introspection
   endpoint.

5.  JWT Response

   The introspection endpoint responds with a JWT, setting the "Content-
   Type" header to "application/jwt".  This JWT is a cryptographically
   protected representation of the token introspection response as
   specified in [RFC7662].

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   Note: Although the JWT format is widely used as an access token
   format, the JWT returned in the introspection response is not an
   alternative representation of the introspected access token and is
   not intended to be used as an access token.

   JWT metadata values, such as "iat", might differ between the token
   introspection response in JWT format and the introspected access
   token (see below).

   This specification registers the "application/token-
   introspection+jwt" media type, which is used as value of the "typ"
   header parameter of the JWT to indicate that the payload is a token
   introspection response.

   If the access token is invalid, expired, has been revoked, or is not
   intended to be consumed by the calling resource server (audience),
   the authorization server MUST set the value of the response claim
   "active" to "false".  Otherwise, this claim is set to "true".

   If the access token is considered active, it MUST contain the claims
   "iss" and "aud" in order to prevent misuse of the JWT as an ID or
   access token (see Section 8.1).

   The "iss" MUST be set to the issuer URL of the AS.

   The value of the "aud" claims MUST identify the resource server
   receiving the token introspection response.

   If the AS adds the following claims to the token introspection
   response their meaning is defined as follows:

   iat     The "iat" claim indicates when the introspection response was
           issued by the AS.

   exp     The "exp" claim indicates when the access token passed in the
           introspection request will expire.

   jti     The "jti" claim is a unique identifier for the access token
           passed in the introspection request.  This identifier MUST be
           stable for all introspection calls for a given access token.

   Further content of the introspection response is determined by the
   RS-specific policy at the AS.

   If possible, the AS MUST narrow down the "scope" value to the scopes
   relevant to the particular RS.

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   The JWT formatted introspection response MAY contain further claims,
   especially the claims defined in the "OAuth Token Introspection
   Response" registry established by [RFC7662] and the "JSON Web Token
   Claims" registry established by [RFC7519].

   This includes claims from the "JSON Web Token Claims" registry that
   are commonly used in [OpenID.Core] and can be applied to the resource
   owner.  These claims can serve to identify the resource owner as a
   natural person or to provide a required contact detail, such as an
   e-Mail address or phone number.  When transmitting such claims the AS
   acts as an identity provider in regard to the RS.

   The AS determines based on the RS-specific policy what claims about
   the resource owner to return in the token introspection response.
   The AS MUST ensure that the release of any privacy-sensitive data is
   legally based.

   The following is a non-normative example response (with line breaks
   for display purposes only):

   HTTP/1.1 200 OK
   Content-Type: application/jwt

   eyJ0eXAiOiJ0b2tlbi1pbnRyb3NwZWN0aW9uK2p3dCIsImFsZyI6IlJTMjU2In0.eyJ
   pc3MiOiJodHRwczovL3NlcnZlci5leGFtcGxlLmNvbS8iLCJhdWQiOiJzNkJoZFJrcX
   QzIiwianRpIjoidDFGb0NDYVpkNFh2NE9SSlVXVlVlVFpmc0toVzMwQ1FDcldERGp3W
   Hk2dyIsImFjdGl2ZSI6dHJ1ZSwic2NvcGUiOiJyZWFkIHdyaXRlIGRvbHBoaW4iLCJl
   eHAiOjE1MTQ3OTc5NDIwMDAsImlhdCI6MTUxNDc5NzgyMjAwMCwiY2xpZW50X2lkIjo
   iczZCaGRSa3F0MyIsInN1YiI6Ilo1TzN1cFBDODhRckFqeDAwZGlzIiwiZ2l2ZW5fbm
   FtZSI6IkpvaG4iLCJmYW1pbHlfbmFtZSI6IkRvZSIsImJpcnRoZGF0ZSI6IjE5ODItM
   DItMDEifQ.mnGNVJJwMaMR-drVHIyjOd7S5mScHT5tYC_sLdeaS9C4pkmiOgwHNGah9
   w_15kbotjDckotJNHpNTQCcE5nRC29L_jz5hSCNTMmK62fJdEcq0QVuCL_roeHzc-s1
   bjU2V2Qme6_2468zqcuhf1fhcieWxx9bDwFFwk3su0qdoF9RBa0HobWzy1ENU6MjiKH
   vmrnd5PkJenn1rJEt0EQTUuVE0vh2tQGhxbaZkQ34mLLgES5TCuBK7ALDXhT4aGCzxg
   3jLprs_jYTjCq2kugptseKaxsvti0TxOxmxLPcuy5xRxHDUzV2h9_VWVJRgM8y0vhLN
   v9XKDe4EQqaIFLA_YD4TBeyPV7Sm4xMQ-2OsSmAz0E2BY_b_s0WrFN2K8tspQhj2mnG
   v7Zz8O3zeE2gC59JR56aU_SNspGPbt8GvTwuL5ZZTCmiWKUzQ0ev4zVthUczQmK53dx
   Zl6ZxBfIRPV5k1GTPyEPbWehizbJT4JBSLlk-l8JvJcfL2USLtJgMLH1D01fww0IqN1
   ofHeHFUmZWB_LR7kGaJ8Kx_a9z4CaaVesW8jzgSmwA8K_pv9yJqqjnUhsh51c49OAgn
   cqwAahGrUhrN0dIBrd6sRXU3AiRpaah0MMNcjR2UJbEZKwnMyHTkBQAeZAe9vO9pKV8
   JOd0ziYBpAbEpYGE4p3wog4

   The example response header contains the following JSON document:

   {
     "typ": "token-introspection+jwt",
     "alg": "RS256"
   }

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   The example response payload contains the following JSON document:

   {
      "iss":"https://server.example.com/",
      "aud":"s6BhdRkqt3",
      "jti": "t1FoCCaZd4Xv4ORJUWVUeTZfsKhW30CQCrWDDjwXy6w",
      "active":true,
      "scope":"read write dolphin",
      "exp":1514797942000,
      "iat":1514797822000,
      "client_id":"s6BhdRkqt3",
      "sub":"Z5O3upPC88QrAjx00dis",
      "given_name":"John",
      "family_name":"Doe",
      "birthdate":"1982-02-01"
   }

   Depending on the specific resource server policy the JWT is either
   signed, or signed and encrypted.  If the JWT is signed and encrypted
   it MUST be a Nested JWT, as defined in JWT [RFC7519].

   Note: If the resource server policy requires a signed and encrypted
   response and the authorization server receives an unauthenticated
   request containing an Accept header with content type other than
   "application/jwt", it MUST refuse to serve the request and return an
   HTTP status code 400.  This is done to prevent downgrading attacks to
   obtain token data intended for release to legitimate recipients only
   (see Section 8.2).

6.  Client Metadata

   The authorization server determines what algorithm to employ to
   secure the JWT for a particular introspection response.  This
   decision can be based on registered metadata parameters for the
   resource server, supplied via dynamic client registration [RFC7591]
   with the resource server acting as a client, as specified below.

   The parameter names follow the pattern established by OpenID Connect
   Dynamic Client Registration [OpenID.Registration] for configuring
   signing and encryption algorithms for JWT responses at the UserInfo
   endpoint.

   The following client metadata parameters are introduced by this
   specification:

   introspection_signed_response_alg  OPTIONAL.  JWS [RFC7515] algorithm
           ("alg" value) as defined in JWA [RFC7518] for signing
           introspection responses.  If this is specified, the response

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           will be signed using JWS and the configured algorithm.  The
           default, if omitted, is "RS256".

   introspection_encrypted_response_alg  OPTIONAL.  JWE [RFC7516]
           algorithm ("alg" value) as defined in JWA [RFC7518] for
           content key encryption.  If this is specified, the response
           will be encrypted using JWE and the configured content
           encryption algorithm
           ("introspection_encrypted_response_enc").  The default, if
           omitted, is that no encryption is performed.  If both signing
           and encryption are requested, the response will be signed
           then encrypted, with the result being a Nested JWT, as
           defined in JWT [RFC7519].

   introspection_encrypted_response_enc  OPTIONAL.  JWE [RFC7516]
           algorithm ("enc" value) as defined in JWA [RFC7518] for
           content encryption of introspection responses.  The default,
           if omitted, is "A128CBC-HS256".  Note: This parameter MUST
           NOT be specified without setting
           "introspection_encrypted_response_alg".

   Resource servers may register their public encryption keys using the
   "jwks_uri" or "jwks" metadata parameters.

7.  Authorization Server Metadata

   Authorization servers SHOULD publish the supported algorithms for
   signing and encrypting the JWT of an introspection response by
   utilizing OAuth 2.0 Authorization Server Metadata [RFC8414]
   parameters.  Resource servers use this data to parametrize their
   client registration requests.

   The following parameters are introduced by this specification:

   introspection_signing_alg_values_supported  OPTIONAL.  JSON array
           containing a list of the JWS [RFC7515] signing algorithms
           ("alg" values) as defined in JWA [RFC7518] supported by the
           introspection endpoint to sign the response.

   introspection_encryption_alg_values_supported  OPTIONAL.  JSON array
           containing a list of the JWE [RFC7516] encryption algorithms
           ("alg" values) as defined in JWA [RFC7518] supported by the
           introspection endpoint to encrypt the content encryption key
           for introspection responses (content key encryption).

   introspection_encryption_enc_values_supported  OPTIONAL.  JSON array
           containing a list of the JWE [RFC7516] encryption algorithms
           ("enc" values) as defined in JWA [RFC7518] supported by the

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           introspection endpoint to encrypt the response (content
           encryption).

8.  Security Considerations

8.1.  Cross-JWT Confusion

   Token introspection responses in JWT format, access tokens in JWT
   format, and OpenID Connect ID Tokens are syntactical similar.
   Attackers could try to utilize this fact and attempt to use a token
   introspection response as access token when invoking a resource
   server or as ID Token when logging into at a OpenID Connect RP.

   Any relying party processing the "typ" JWT header element should
   detect the attack since token introspection responses in JWT format
   set this header to the value "token-introspection+jwt".
   Unfortunately, this is not a well established practice yet.

   As an alternative approach, such an attack can be prevented like any
   other token substitution attack by restricting the audience of the
   JWT.  As specified in Section 5, the authorization server includes
   the claims "iss" and "aud" in each JWT introspection response, with
   the "iss" value set to the authorization server's issuer URL and the
   "aud" value set to the resource server's identifier.  Any recipient
   of an JWT MUST check these values in order to detect substitution
   attacks.

   OpenID Connect RPs are additionally expected to use and check the
   "nonce" parameter and claim to prevent token and code replay.

   Resource servers MUST additionally apply the countermeasures against
   replay as described in [I-D.ietf-oauth-security-topics], section 3.2.

   JWT Confusion and other attacks involving JWTs are discussed in
   [I-D.ietf-oauth-jwt-bcp].

8.2.  Token Data Leakage

   The authorization server MUST use Transport Layer Security (TLS) 1.2
   (or higher) per BCP 195 [RFC7525] in order to prevent token data
   leakage.

   To prevent introspection of leaked tokens and to present an
   additional security layer against token guessing attacks the
   authorization server MAY require all requests to the token
   introspection endpoint to be authenticated.  As an alternative or as
   an addition to the authentication, the intended recipients MAY be set
   up for encrypted responses.

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   In the latter case, confidentiality is ensured by the fact that only
   the legitimate recipient is able to decrypt the response.  An
   attacker could try to circumvent this measure by requesting a plain
   JSON response, using an Accept header with the content type set to,
   for example, "application/json" instead of "application/jwt".  To
   prevent this attack the authorization server MUST NOT serve requests
   with a content type other than "application/jwt" if the resource
   server is set up to receive encrypted responses (see also Section 5).

8.3.  Keeping Token Data Confidential from OAuth Clients

   Authorization servers with a policy that requires token data to be
   kept confidential from OAuth clients must require all requests to the
   token introspection endpoint to be authenticated.  As an alternative
   or as an addition to the authentication, the intended recipients may
   be set up for encrypted responses.

8.4.  Logging and Audit of Introspection Activity

   Authorization servers with a policy that requires token introspection
   activity to be logged and audited must require all requests to the
   token introspection endpoint to be authenticated.

9.  Privacy Considerations

   The token introspection response can be used to transfer personal
   identifiable information from the AS to the RS.  The AS MUST ensure a
   legal basis exists for the data transfer before any data is released
   to a particular RS.  The way the legal basis is established might
   vary among jurisdictions and MUST consider the legal entities
   involved.

   For example, the classical way to establish the legal basis is by
   explicit user consent gathered from the resource owner by the AS
   during the authorization flow.

   It is also possible that the legal basis is established out of band,
   e.g. in an explicit contract or by the client gathering the resource
   owner's consent.

   If the AS and the RS belong to the same legal entity (1st party
   scenario), there is potentially no need for an explicit user consent
   but the terms of service and policy of the respective service
   provider MUST be enforced at all times.

   In any case, the AS MUST ensure that the scope of the legal basis is
   enforced throughout the whole process.  The AS MUST retain the scope
   of the legal basis with the access token, e.g. in the scope value,

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   and the AS MUST determine the data a resource server is allowed to
   receive based on the resource server's identity and suitable token
   data, e.g. the scope value.

10.  Acknowledgements

   We would like to thank Petteri Stenius, Neil Madden, Filip Skokan,
   Tony Nadalin, and Remco Schaar for their valuable feedback.

11.  IANA Considerations

11.1.  OAuth Dynamic Client Registration Metadata Registration

   This specification requests registration of the following client
   metadata definitions in the IANA "OAuth Dynamic Client Registration
   Metadata" registry [IANA.OAuth.Parameters] established by [RFC7591]:

11.1.1.  Registry Contents

   o  Client Metadata Name: "introspection_signed_response_alg"

   o  Client Metadata Description: String value indicating the client's
      desired introspection response signing algorithm.

   o  Change Controller: IESG

   o  Specification Document(s): Section 6 of [[ this specification ]]

   o  Client Metadata Name: "introspection_encrypted_response_alg"

   o  Client Metadata Description: String value specifying the desired
      introspection response content key encryption algorithm (alg
      value).

   o  Change Controller: IESG

   o  Specification Document(s): Section 6 of [[ this specification ]]

   o  Client Metadata Name: "introspection_encrypted_response_enc"

   o  Client Metadata Description: String value specifying the desired
      introspection response content encryption algorithm (enc value).

   o  Change Controller: IESG

   o  Specification Document(s): Section 6 of [[ this specification ]]

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11.2.  OAuth Authorization Server Metadata Registration

   This specification requests registration of the following values in
   the IANA "OAuth Authorization Server Metadata" registry
   [IANA.OAuth.Parameters] established by [RFC8414].

11.2.1.  Registry Contents

   o  Metadata Name: "introspection_signing_alg_values_supported"

   o  Metadata Description: JSON array containing a list of algorithms
      supported by the authorization server for introspection response
      signing.

   o  Change Controller: IESG

   o  Specification Document(s): Section 7 of [[ this specification ]]

   o  Metadata Name: "introspection_encryption_alg_values_supported"

   o  Metadata Description: JSON array containing a list of algorithms
      supported by the authorization server for introspection response
      content key encryption (alg value).

   o  Change Controller: IESG

   o  Specification Document(s): Section 7 of [[ this specification ]]

   o  Metadata Name: "introspection_encryption_enc_values_supported"

   o  Metadata Description: JSON array containing a list of algorithms
      supported by the authorization server for introspection response
      content encryption (enc value).

   o  Change Controller: IESG

   o  Specification Document(s): Section 7 of [[ this specification ]]

11.3.  Media Type Registration

   This section registers the "application/token-introspection+jwt"
   media type in the "Media Types" registry [IANA.MediaTypes] in the
   manner described in [RFC6838], which can be used to indicate that the
   content is a token introspection response in JWT format.

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11.3.1.  Registry Contents

   o  Type name: application

   o  Subtype name: token-introspection+jwt

   o  Required parameters: N/A

   o  Optional parameters: N/A

   o  Encoding considerations: binary; A token introspection response is
      a JWT; JWT values are encoded as a series of base64url-encoded
      values (with trailing '=' characters removed), some of which may
      be the empty string, separated by period ('.') characters.

   o  Security considerations: See Section 7 of this specification

   o  Interoperability considerations: N/A

   o  Published specification: Section 4 of this specification

   o  Applications that use this media type: Applications that produce
      and consume OAuth Token Introspection Responses in JWT format

   o  Fragment identifier considerations: N/A

   o  Additional information:

      *  Magic number(s): N/A

      *  File extension(s): N/A

      *  Macintosh file type code(s): N/A

   o  Person & email address to contact for further information: Torsten
      Lodderstedt, torsten@lodderstedt.net

   o  Intended usage: COMMON

   o  Restrictions on usage: none

   o  Author: Torsten Lodderstedt, torsten@lodderstedt.net

   o  Change controller: IESG

   o  Provisional registration?  No

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12.  References

12.1.  Normative References

   [I-D.ietf-oauth-jwt-bcp]
              Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
              Current Practices", draft-ietf-oauth-jwt-bcp-06 (work in
              progress), June 2019.

   [I-D.ietf-oauth-security-topics]
              Lodderstedt, T., Bradley, J., Labunets, A., and D. Fett,
              "OAuth 2.0 Security Best Current Practice", draft-ietf-
              oauth-security-topics-13 (work in progress), July 2019.

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

   [OpenID.Core]
              Sakimura, N., Bradley, J., Jones, M., Medeiros, B. D., and
              C. Mortimore, "OpenID Connect Core 1.0 incorporating
              errata set 1", Nov 2014,
              <http://openid.net/specs/openid-connect-core-1_0.html>.

   [OpenID.Registration]
              Sakimura, N., Bradley, J., and M. Jones, "OpenID Connect
              Dynamic Client Registration 1.0 incorporating errata set
              1", Nov 2014, <https://openid.net/specs/
              openid-connect-registration-1_0.html>.

   [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>.

   [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>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <https://www.rfc-editor.org/info/rfc7516>.

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   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [RFC7519]  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>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC7591]  Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
              P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
              RFC 7591, DOI 10.17487/RFC7591, July 2015,
              <https://www.rfc-editor.org/info/rfc7591>.

   [RFC7662]  Richer, J., Ed., "OAuth 2.0 Token Introspection",
              RFC 7662, DOI 10.17487/RFC7662, October 2015,
              <https://www.rfc-editor.org/info/rfc7662>.

   [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>.

12.2.  Informative References

   [IANA.OAuth.Parameters]
              IANA, "OAuth Parameters",
              <http://www.iana.org/assignments/oauth-parameters>.

Appendix A.  Document History

   [[ To be removed from the final specification ]]

   -08

   o  made difference between introspected access token and
      introspection response clearer

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   o  defined semantics of JWT claims overlapping between introspected
      access token and introspection response as JWT

   o  added section about RS management

   o  added text about user claims including a privacy considerations
      section

   o  removed registration of OpenID Connect claims to "Token
      Introspection Response" registry and refer to "JWT Claims"
      registry instead

   o  added registration of "application/token-introspection+jwt" media
      type as type identifier of token introspection responses in JWT
      format

   o  more changed to incorporate IESG review feedback

   -07

   o  fixed wrong description of "locale"

   o  added references for ISO and ITU specifications

   -06

   o  replaced reference to RFC 7159 with reference to RFC 8259

   -05

   o  improved wording for TLS requirement

   o  added RFC 2119 boilerplate

   o  fixed and updated some references

   -04

   o  reworked definition of parameters in section 4

   o  added text on data minimization to security considerations section

   o  added statement regarding TLS to security considerations section

   -03

   o  added registration for OpenID Connect Standard Claims to OAuth
      Token Introspection Response registry

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   -02

   o  updated references

   -01

   o  adapted wording to preclude any accept header except "application/
      jwt" if encrypted responses are required

   o  use registered alg value RS256 for default signing algorithm

   o  added text on claims in the token introspection response

   -00

   o  initial version of the WG draft

   o  defined default signing algorithm

   o  changed behavior in case resource server is set up for encryption

   o  Added text on token data leakage prevention to the security
      considerations

   o  moved Security Considerations section forward

   WG draft

   -01

   o  fixed typos in client meta data field names

   o  added OAuth Server Metadata parameters to publish algorithms
      supported for signing and encrypting the introspection response

   o  added registration of new parameters for OAuth Server Metadata and
      Client Registration

   o  added explicit request for JWT introspection response

   o  made iss and aud claims mandatory in introspection response

   o  Stylistic and clarifying edits, updates references

   -00

   o  initial version

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Authors' Addresses

   Torsten Lodderstedt (editor)
   yes.com AG

   Email: torsten@lodderstedt.net

   Vladimir Dzhuvinov
   Connect2id Ltd.

   Email: vladimir@connect2id.com

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