OAuth Working Group M. Jones Internet-Draft Microsoft Intended status: Standards Track November 3, 2013 Expires: May 7, 2014 OAuth 2.0 Token Exchange draft-jones-oauth-token-exchange-00 Abstract This specification defines how to request and obtain Security Tokens from OAuth Authorization Servers, including enabling one party to act on behalf of another or enabling one party to delegate authority to another. 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 http://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 May 7, 2014. Copyright Notice Copyright (c) 2013 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 (http://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. Jones Expires May 7, 2014 [Page 1] Internet-Draft OAuth 2.0 Token Exchange November 2013 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Notation and Conventions . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. On-Behalf-Of vs. Impersonation Semantics . . . . . . . . . 3 2. Security Token Request . . . . . . . . . . . . . . . . . . . . 4 2.1. Act-As Security Token Requests . . . . . . . . . . . . . . 5 2.2. On-Behalf-Of Security Token Requests . . . . . . . . . . . 5 3. Security Token Response . . . . . . . . . . . . . . . . . . . . 6 4. Conveying Eligibility to Act As Another Party . . . . . . . . . 6 5. Implementation Considerations . . . . . . . . . . . . . . . . . 7 6. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . . 8 Appendix A. Document History . . . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 Jones Expires May 7, 2014 [Page 2] Internet-Draft OAuth 2.0 Token Exchange November 2013 1. Introduction This specification defines how to request and obtain Security Tokens from OAuth Authorization Servers [RFC6749], including enabling one party to act on behalf of another or enabling one party to delegate authority to another. This functionality is intentionally parallel to the functionality defined by [WS-Trust], including On-Behalf-Of and Act-As. A Security Token is a set of information that facilitates the sharing of identity and security information across security domains. Examples of Security Tokens include JSON Web Tokens (JWTs) [JWT] and SAML Assertions [OASIS.saml-core-2.0-os]. Security Tokens are typically signed to achieve integrity and sometimes also encrypted to achieve confidentiality. Security Tokens are also described as Assertions in [I-D.ietf-oauth-assertions]. This specification defines a new Security Token Request Grant Type used at the Token Endpoint to convey the parameters for a Security Token request and Security Token response parameter used in responses to these requests. The Security Token Request is a JSON Web Token (JWT) [JWT] that is signed by the requesting party that contains parameters of the request as Claims. The Security Tokens obtained could be used in a number of contexts, the specifics of which are beyond the scope of this specification. Examples include using them with the 1.1. Requirements Notation and Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 1.2. Terminology This specification uses the terms "Authorization Server" "Token Endpoint", "Token Request", and "Token Response" defined by OAuth 2.0 [RFC6749], and the terms "Claim" and "JWT Claims Set" defined by JSON Web Token (JWT) [JWT]. 1.3. On-Behalf-Of vs. Impersonation Semantics When principal A acts on behalf of principal B, A is given all the rights that B has within some defined rights context. Whereas, with on-behalf-of semantics, principal A still has its own identity separate from B and it is explicitly understood that while B may have delegated its rights to A, any actions taken are being taken by A and Jones Expires May 7, 2014 [Page 3] Internet-Draft OAuth 2.0 Token Exchange November 2013 not B. In a sense, A is an agent for B. On-behalf-of semantics are therefore different than impersonation semantics, with which it is sometimes confused. When principal A impersonates principal B, then in so far as any entity receiving Claims is concerned, they are actually dealing with B. It is true that some members of the identity system might have awareness that impersonation is going on but it is not a requirement. For all intents and purposes, when A is acting for B, A is B. 2. Security Token Request A Security Token Request is sent to the Token Endpoint as a Token Request message using this Grant Type value: security_token_request Grant Type value indicating that this Token Request is a Security Token Request. A Token Request parameter of the same name is used to convey the information contained in Security Token Request as a JWT: security_token_request Token Request parameter whose value is a JWT containing the Security Token Request information. An example Security Token Request (with extra line breaks for display purposes only) follows: POST /token HTTP/1.1 Host: server.example.com Content-Type: application/x-www-form-urlencoded grant_type=security_token_request&security_token_request= eyJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJ ... [omitted for brevity] The "security_token_request" parameter value is a JWT with the following members: iss REQUIRED. The issuer of the principal requesting the Security Token. sub REQUIRED. The identifier of the principal requesting the Security Token at the issuer. security_token_type OPTIONAL. An identifier for the type of the requested Security Token. If not present, the default is that a JWT is being requested. A JWT can also be requested with the identifier "urn:ietf:params:oauth:token-type:jwt". Jones Expires May 7, 2014 [Page 4] Internet-Draft OAuth 2.0 Token Exchange November 2013 scopes OPTIONAL. An array of strings, each of which represents a service context that the requested Security Token is being requested to be used for. The array MUST contain at least one scope value. The definition of these contexts is outside the scope of this specification. (Note: This request element serves the same purpose as the WS-Trust AppliesTo RST element.) The JWT MUST be signed by the issuer so the identity of the requesting party can be validated. The following is an example of a JWT Claims Set for a Security Token Request: { "iss": "https://server.example.com", "sub": "24400320", "scopes": ["example"] } 2.1. Act-As Security Token Requests This specification defines the ability to request a Security Token for the requesting party to use to act as the specified party. This is accomplished using this Token Request parameter: act_as This OPTIONAL request parameter indicates that the requested Security Token is expected to contain information about the identity represented by the Security Token that is the value of this parameter, enabling the requesting party to use the returned Security Token to act as this identity. The following is an example of a JWT Claims Set for a Security Token Request using an "act_as" Claim: { "iss": "https://server.example.com", "sub": "24400320", "scopes": ["example"], "act_as": "eyJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJ ..." } 2.2. On-Behalf-Of Security Token Requests This specification defines the ability to request a Security Token on behalf of another party. This is accomplished using this Token Request parameter: Jones Expires May 7, 2014 [Page 5] Internet-Draft OAuth 2.0 Token Exchange November 2013 on_behalf_of This OPTIONAL request parameter indicates that the Security Token is being requested on behalf of another party. The identity of the party upon whose behalf the request is being made is represented by the Security Token that is the value of this parameter. Proof of eligibility to act on behalf of that identity MAY be conveyed by including an "actor" Claim identifying the requesting party in the Security Token, per Section 4, provided the Security Token is a JWT. The following is an example of a JWT Claims Set for a Security Token Request using an "on_behalf_of" Claim: { "iss": "https://server.example.com", "sub": "24400320", "scopes": ["example"], "on_behalf_of": "eyJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJ ..." } 3. Security Token Response A Security Token Response is returned from the Token Endpoint as a Token Response message containing these members: security_token The returned Security Token. security_token_type An identifier for the type of the returned Security Token. If the Security Token is a JWT, this identifier is "urn:ietf:params:oauth:token-type:jwt". An example successful response is as follows: HTTP/1.1 200 OK Content-Type: application/json;charset=UTF-8 Cache-Control: no-store Pragma: no-cache { "security_token": "eyJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJ ...", "security_token_type": "urn:ietf:params:oauth:token-type:jwt" } 4. Conveying Eligibility to Act As Another Party It is useful to be able to make a statement that one party is authorized to act on behalf of another party. This can be done by Jones Expires May 7, 2014 [Page 6] Internet-Draft OAuth 2.0 Token Exchange November 2013 having the party being acted for sign a Security Token containing a Claim identifying party that will act for it as an authorized actor. This statement can also optionally identify scopes in which the actor is eligible to act through another Claim. The following Claims are defined for use in JWTs for these purposes: actor Security Token that identifies a party who is asserted as being eligible to act for the party identified by the JWT containing this Claim. scopes OPTIONAL. An array of strings, each of which represents a service context for which the actor is asserted as being eligible to act for the party identified by the JWT containing this Claim. The array MUST contain at least one scope value. The definition of these contexts is outside the scope of this specification. 5. Implementation Considerations Implementations of the specification MUST implement support for using JWTs as the Security Tokens. Other Security Token types MAY be supported. 6. Open Issues The following decisions need to be made and updates this spec performed: o Should we say anything about proof of possession of the target party's key in the On-Behalf-Of case beyond specifying the use of the "actor" Claim? o Revise the text in the On-Behalf-Of vs. Impersonation Semantics section to better align the terminology used with the semantics specified. 7. IANA Considerations The "security_token_request" Grant Type is to be registered in the OAuth Parameters registry. The "scopes", "act_as", and "on_behalf_of" Claims are to be registered in the JSON Web Token Claims registry. Jones Expires May 7, 2014 [Page 7] Internet-Draft OAuth 2.0 Token Exchange November 2013 8. Security Considerations All of the normal security issues, especially in relationship to comparing URIs and dealing with unrecognized values, that are discussed in JWT [JWT] also apply here. In addition, on-behalf-of introduces its own unique security issues. Any time one principal is delegated the rights of another principal, the potential for abuse is always a concern. That is why use of the "scopes" member is suggested. The scope values restrict the contexts in which the delegated rights can be exercised. 9. References 9.1. Normative References [JWT] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", draft-ietf-oauth-json-web-token (work in progress), October 2013. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 6749, October 2012. 9.2. Informative References [I-D.ietf-oauth-assertions] Campbell, B., Mortimore, C., Jones, M., and Y. Goland, "Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants", draft-ietf-oauth-assertions (work in progress), July 2013. [OASIS.saml-core-2.0-os] Cantor, S., Kemp, J., Philpott, R., and E. Maler, "Assertions and Protocol for the OASIS Security Assertion Markup Language (SAML) V2.0", OASIS Standard saml-core- 2.0-os, March 2005. [WS-Trust] Nadalin, A., Goodner, M., Gudgin, M., Barbir, A., and H. Granqvist, "WS-Trust 1.4", February 2012, . Jones Expires May 7, 2014 [Page 8] Internet-Draft OAuth 2.0 Token Exchange November 2013 Appendix A. Document History [[ to be removed by the RFC Editor before publication as an RFC ]] -00 o Created initial version. Author's Address Michael B. Jones Microsoft Email: mbj@microsoft.com URI: http://self-issued.info/ Jones Expires May 7, 2014 [Page 9]