Open Authentication Protocol T. Lodderstedt, Ed.
Internet-Draft AG
Intended status: Standards Track V. Dzhuvinov
Expires: August 23, 2019 Connect2id Ltd.
February 19, 2019

JWT Response for OAuth Token Introspection


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

Status of This Memo

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Table of Contents

1. Introduction

OAuth 2.0 Token Introspection 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 allows deployments to implement identifier-based access tokens in an interoperable way.

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

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

2. 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.

The following is a non-normative example request:

POST /introspect HTTP/1.1
Accept: application/jwt
Content-Type: application/x-www-form-urlencoded


3. JWT Response

The introspection endpoint responds with a JWT, setting the Content-Type header to "application/jwt".

This JWT MUST contain the claims iss and aud in order to prevent misuse of the JWT as ID or access token (see Section 6.1).

This JWT MAY furthermore contain all other claims described in Section 2.2. of [RFC7662] and beyond (e.g. as defined in [OpenID.Core]).

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

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


The example response contains the following JSON document:

  "sub": "Z5O3upPC88QrAjx00dis",
  "aud": "",
  "scope": "read write dolphin",
  "iss": "",
  "active": true,
  "exp": 1419356238,
  "iat": 1419350238,
  "client_id": "l238j323ds-23ij4",
  "given_name": "John",

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.

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 6.2).

4. 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 with the resource server posing as the client, as defined by this draft.

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

The following client metadata parameters are introduced by this specification:

JWS alg algorithm JWA REQUIRED for signing introspection responses. If this is specified, the response will be signed using JWS and the configured algorithm. The default, if omitted, is RS256.
JWE alg algorithm JWA REQUIRED for encrypting introspection responses. 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. The default, if omitted, is that no encryption is performed.
JWE enc algorithm JWA REQUIRED for encrypting introspection responses. If introspection_encrypted_response_alg is specified, the default for this value is A128CBC-HS256. When introspection_encrypted_response_enc is included, introspection_encrypted_response_alg MUST also be provided.

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

5. 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 parameters.

The following parameters are introduced by this specification:

OPTIONAL. JSON array containing a list of the JWS signing algorithms (alg values) JWA supported by the introspection endpoint to sign the response.
OPTIONAL. JSON array containing a list of the JWE encryption algorithms (alg values) JWA supported by the introspection endpoint to encrypt the response.
OPTIONAL. JSON array containing a list of the JWE encryption algorithms (enc values) JWA supported by the introspection endpoint to encrypt the response.

6. Security Considerations

6.1. Cross-JWT Confusion

JWT introspection responses and OpenID Connect ID Tokens are syntactically similar. An attacker could therefore attempt to impersonate an end-user at a OpenID Connect relying party by passing the JWT as an ID token.

Such an attack can be prevented like any other token substitution attack. The authorization server MUST include 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. This allows a correctly implemented OpenID Connect relying party to detect substitution by checking the iss and aud claims as described in Section of [OpenID.Core]. Relying parties SHOULD also use and check the nonce parameter and claim to prevent token and code replay.

Resource servers utilizing JWTs to represent structured access tokens could be susceptible to replay attacks. Resource servers should therefore apply proper counter measures against replay as described in [I-D.ietf-oauth-security-topics], section 2.2.

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

6.2. Token Data Leakage

If the authorization server supports unauthenticated requests an attacker could potentially retrieve token data which must be kept confidential. This attack can be prevented by either authenticating any request to the token introspection endpoint or by setting up the respective recipient for encrypted responses.

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 content type other than "application/jwt" if the resource server is set up to receive encrypted responses (see also Section 3).

7. Acknowledgements

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

8. IANA Considerations

8.1. 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]:

8.1.1. Registry Contents

8.2. OAuth Authorization Server Metadata Registration

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

8.2.1. Registry Contents

8.3. OAuth Token Introspection Response

TBD: add all OpenID Connect standard claims.

9. References

9.1. Normative References

[I-D.ietf-oauth-jwt-bcp] Sheffer, Y., Hardt, D. and M. Jones, "JSON Web Token Best Current Practices", Internet-Draft draft-ietf-oauth-jwt-bcp-04, November 2018.
[I-D.ietf-oauth-security-topics] Lodderstedt, T., Bradley, J., Labunets, A. and D. Fett, "OAuth 2.0 Security Best Current Practice", Internet-Draft draft-ietf-oauth-security-topics-11, December 2018.
[OpenID.Core] NRI, Ping Identity, Microsoft, Google and Salesforce, "OpenID Connect Core 1.0 incorporating errata set 1", Nov 2014.
[OpenID.Registration] NRI, Ping Identity and Microsoft, "OpenID Connect Dynamic Client Registration 1.0 incorporating errata set 1", Nov 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, DOI 10.17487/RFC2246, January 1999.
[RFC7515] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", RFC 7516, DOI 10.17487/RFC7516, May 2015.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, May 2015.
[RFC7519] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015.
[RFC7591] Richer, J., Jones, M., Bradley, J., Machulak, M. and P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol", RFC 7591, DOI 10.17487/RFC7591, July 2015.
[RFC7662] Richer, J., "OAuth 2.0 Token Introspection", RFC 7662, DOI 10.17487/RFC7662, October 2015.
[RFC8414] Jones, M., Sakimura, N. and J. Bradley, "OAuth 2.0 Authorization Server Metadata", RFC 8414, DOI 10.17487/RFC8414, June 2018.

9.2. Informative References

[IANA.OAuth.Parameters] IANA, "OAuth Parameters"

Appendix A. Document History

[[ To be removed from the final specification ]]




WG draft



Authors' Addresses

Torsten Lodderstedt (editor) AG EMail:
Vladimir Dzhuvinov Connect2id Ltd. EMail: