Open Authentication Protocol T. Lodderstedt, Ed. Internet-Draft yes.com AG Intended status: Standards Track V. Dzhuvinov Expires: August 23, 2019 Connect2id Ltd. February 19, 2019 JWT Response for OAuth Token Introspection draft-ietf-oauth-jwt-introspection-response-02 Abstract This draft proposes an additional JSON Web Token (JWT) based 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 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 August 23, 2019. 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 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 extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 1] Internet-Draft JWT Response February 2019 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Requesting a JWT Response . . . . . . . . . . . . . . . . . . 3 3. JWT Response . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Client Metadata . . . . . . . . . . . . . . . . . . . . . . . 4 5. Authorization Server Metadata . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6.1. Cross-JWT Confusion . . . . . . . . . . . . . . . . . . . 5 6.2. Token Data Leakage . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8.1. OAuth Dynamic Client Registration Metadata Registration . 7 8.1.1. Registry Contents . . . . . . . . . . . . . . . . . . 7 8.2. OAuth Authorization Server Metadata Registration . . . . 7 8.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 7 8.3. OAuth Token Introspection Response . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 10 Appendix A. Document History . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 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 allows deployments to implement identifier-based 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 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. Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 2] Internet-Draft JWT Response February 2019 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 Host: server.example.com Accept: application/jwt Content-Type: application/x-www-form-urlencoded token=2YotnFZFEjr1zCsicMWpAA 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 eyJraWQiOiIxIiwiYWxnIjoiUlMyNTYifQ.eyJzdWIiOiJaNU8zdXBQQzg4UXJBa ngwMGRpcyIsImF1ZCI6Imh0dHBzOlwvXC9wcm90ZWN0ZWQuZXhhbXBsZS5uZXRcL 3Jlc291cmNlIiwiZXh0ZW5zaW9uX2ZpZWxkIjoidHdlbnR5LXNldmVuIiwic2Nvc GUiOiJyZWFkIHdyaXRlIGRvbHBoaW4iLCJpc3MiOiJodHRwczpcL1wvc2VydmVyL mV4YW1wbGUuY29tXC8iLCJhY3RpdmUiOnRydWUsImV4cCI6MTQxOTM1NjIzOCwia WF0IjoxNDE5MzUwMjM4LCJjbGllbnRfaWQiOiJsMjM4ajMyM2RzLTIzaWo0Iiwid XNlcm5hbWUiOiJqZG9lIn0.HEQHf05vqVvWVnWuEjbzUnPz6JDQVR69QkxgzBNq5 kk-sK54ieg1STazXGsdFAT8nUhiiV1f_Z4HOKNnBs8TLKaFXokhA0MqNBOYI--2u nVHDqI_RPmC3p0NmP02Xmv4hzxFmTmpgjSy3vpKQDihOjhwNBh7G81JNaJqjJQTR v_1dHUPJotQjMK3k8_5FyiO2p64Y2VyxyQn1VWVlgOHlJwhj6BaGHk4Qf5F8DHQZ 1WCPg2p_-hwfINfXh1_buSjxyDRF4oe9pKy6ZB3ejh9qIMm-WrwltuU1uWMXxN6e S6tUtpKo8UCHBwLWCHmJN7KU6ZojmaISspdS23lELAlyw The example response contains the following JSON document: Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 3] Internet-Draft JWT Response February 2019 { "sub": "Z5O3upPC88QrAjx00dis", "aud": "https://protected.example.net/resource", "scope": "read write dolphin", "iss": "https://server.example.com/", "active": true, "exp": 1419356238, "iat": 1419350238, "client_id": "l238j323ds-23ij4", "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 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 [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 JWS [RFC7515] "alg" algorithm JWA [RFC7518] 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". Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 4] Internet-Draft JWT Response February 2019 introspection_encrypted_response_alg JWE [RFC7516] "alg" algorithm JWA [RFC7518] 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 [RFC7519]. The default, if omitted, is that no encryption is performed. introspection_encrypted_response_enc JWE [RFC7516] "enc" algorithm JWA [RFC7518] 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 [RFC8414] parameters. 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) 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) JWA [RFC7518] supported by the introspection endpoint to encrypt the response. introspection_encryption_enc_values_supported OPTIONAL. JSON array containing a list of the JWE [RFC7516] encryption algorithms ("enc" values) JWA [RFC7518] 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 Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 5] Internet-Draft JWT Response February 2019 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 3.1.3.7. 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 Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 6] Internet-Draft JWT Response February 2019 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 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 4 of [[ this specification ]] o Client Metadata Name: "introspection_encrypted_response_alg" o Client Metadata Description: String value specifying the desired introspection response encryption algorithm (alg value). o Change Controller: IESG o Specification Document(s): Section 4 of [[ this specification ]] o Client Metadata Name: "introspection_encrypted_response_enc" o Client Metadata Description: String value specifying the desired introspection response encryption algorithm (enc value). o Change Controller: IESG o Specification Document(s): Section 4 of [[ this specification ]] 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 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. Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 7] Internet-Draft JWT Response February 2019 o Change Controller: IESG o Specification Document(s): Section 5 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 encryption (alg value). o Change Controller: IESG o Specification Document(s): Section 5 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 encryption (enc value). o Change Controller: IESG o Specification Document(s): Section 5 of [[ this specification ]] 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", draft-ietf-oauth-jwt-bcp-04 (work in progress), November 2018. [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-11 (work in progress), December 2018. [OpenID.Core] NRI, Ping Identity, Microsoft, Google, and Salesforce, "OpenID Connect Core 1.0 incorporating errata set 1", Nov 2014, . Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 8] Internet-Draft JWT Response February 2019 [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., 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, . [RFC7662] Richer, J., Ed., "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, . Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 9] Internet-Draft JWT Response February 2019 9.2. Informative References [IANA.OAuth.Parameters] IANA, "OAuth Parameters", . Appendix A. Document History [[ To be removed from the final specification ]] -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 Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 10] Internet-Draft JWT Response February 2019 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 Authors' Addresses Torsten Lodderstedt (editor) yes.com AG Email: torsten@lodderstedt.net Vladimir Dzhuvinov Connect2id Ltd. Email: vladimir@connect2id.com Lodderstedt & Dzhuvinov Expires August 23, 2019 [Page 11]