[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-jones-oauth-token-exchange) 00 01 02 03 04 05 06 07 08 09

OAuth Working Group                                             M. Jones
Internet-Draft                                                A. Nadalin
Intended status: Standards Track                                C. Baker
Expires: February 22, 2015                                     Microsoft
                                                         August 21, 2014


                        OAuth 2.0 Token Exchange
                   draft-ietf-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 February 22, 2015.

Copyright Notice

   Copyright (c) 2014 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, et al.           Expires February 22, 2015               [Page 1]


Internet-Draft          OAuth 2.0 Token Exchange             August 2014


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 . . . . . . . . . . .  6
   3.  Security Token Response  . . . . . . . . . . . . . . . . . . .  6
   4.  Conveying Eligibility to Act As Another Party  . . . . . . . .  7
   5.  Implementation Considerations  . . . . . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     8.1.  Normative References . . . . . . . . . . . . . . . . . . .  8
     8.2.  Informative References . . . . . . . . . . . . . . . . . .  8
   Appendix A.  Open Issues . . . . . . . . . . . . . . . . . . . . .  9
   Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . .  9
   Appendix C.  Document History  . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10






























Jones, et al.           Expires February 22, 2015               [Page 2]


Internet-Draft          OAuth 2.0 Token Exchange             August 2014


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.  The functionality defined and the terminology
   used in this specification are intentionally parallel to the
   functionality and terminology 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 issued 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



Jones, et al.           Expires February 22, 2015               [Page 3]


Internet-Draft          OAuth 2.0 Token Exchange             August 2014


   delegated its rights to A, any actions taken are being taken by A and
   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:

   urn:ietf:params:oauth:grant-type:security-token-request
      Grant Type value indicating that this Token Request is a Security
      Token Request.

   A Token Request parameter with a related 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=urn:ietf:params:oauth: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.  Issuer of the principal requesting the Security Token.







Jones, et al.           Expires February 22, 2015               [Page 4]


Internet-Draft          OAuth 2.0 Token Exchange             August 2014


   sub
      REQUIRED.  Identifier of the principal requesting the Security
      Token at the issuer.

   security_token_type
      OPTIONAL.  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".

   scopes
      OPTIONAL.  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 request JWT MUST be signed by the issuer so the identity of the
   requesting party can be validated unless the identity of the
   requesting party is known to the Authorization Server by other means;
   in that case, the JWT can use the "alg" value "none".

   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.







Jones, et al.           Expires February 22, 2015               [Page 5]


Internet-Draft          OAuth 2.0 Token Exchange             August 2014


   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:

   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
      Returned Security Token.







Jones, et al.           Expires February 22, 2015               [Page 6]


Internet-Draft          OAuth 2.0 Token Exchange             August 2014


   security_token_type
      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
   having the party being acted for issue a Security Token containing a
   Claim identifying the 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.  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.

   The JWT issued by the party being acted for MUST be signed so the
   identity of the party being acted for can be validated unless the
   identity of the party being acted for is known to the Authorization
   Server by other means; in that case, the JWT can use the "alg" value
   "none".






Jones, et al.           Expires February 22, 2015               [Page 7]


Internet-Draft          OAuth 2.0 Token Exchange             August 2014


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.  IANA Considerations

   The "urn:ietf:params:oauth:grant-type:security-token-request" Grant
   Type is to be registered in the IANA urn:ietf:params:oauth registry
   established in An IETF URN Sub-Namespace for OAuth [RFC6755].

   The "scopes", "act_as", and "on_behalf_of" Claims are to be
   registered in the JSON Web Token Claims registry.


7.  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.


8.  References

8.1.  Normative References

   [JWT]      Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", draft-ietf-oauth-json-web-token (work in
              progress), July 2014.

   [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.

8.2.  Informative References

   [I-D.ietf-oauth-assertions]
              Campbell, B., Mortimore, C., Jones, M., and Y. Goland,



Jones, et al.           Expires February 22, 2015               [Page 8]


Internet-Draft          OAuth 2.0 Token Exchange             August 2014


              "Assertion Framework for OAuth 2.0 Client Authentication
              and Authorization Grants", draft-ietf-oauth-assertions
              (work in progress), April 2014.

   [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.

   [RFC6755]  Campbell, B. and H. Tschofenig, "An IETF URN Sub-Namespace
              for OAuth", RFC 6755, October 2012.

   [WS-Trust]
              Nadalin, A., Goodner, M., Gudgin, M., Barbir, A., and H.
              Granqvist, "WS-Trust 1.4", February 2012, <http://
              docs.oasis-open.org/ws-sx/ws-trust/v1.4/ws-trust.html>.


Appendix A.  Open Issues

   The following decisions need to be made and updates on 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.

   o  Address the sources of potential terminological confusion
      discussed in John Bradley's review comments.

   o  Add examples illustrating concrete uses of act-as and
      on-behalf-of.


Appendix B.  Acknowledgements

   The authors wish to thank Brian Campbell and John Bradley for reviews
   of the specification.


Appendix C.  Document History

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



Jones, et al.           Expires February 22, 2015               [Page 9]


Internet-Draft          OAuth 2.0 Token Exchange             August 2014


   -00

   o  Created initial working group draft from
      draft-jones-oauth-token-exchange-01.


Authors' Addresses

   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/


   Anthony Nadalin
   Microsoft

   Email: tonynad@microsoft.com


   Caleb Baker
   Microsoft

   Email: calebb@microsoft.com


























Jones, et al.           Expires February 22, 2015              [Page 10]


Html markup produced by rfcmarkup 1.123, available from https://tools.ietf.org/tools/rfcmarkup/