Network Working Group M. Jones, Ed. Internet-Draft Microsoft Intended status: Standards Track E. Hammer-Lahav Expires: June 3, 2011 Yahoo! D. Hardt independent D. Recordon Facebook November 30, 2010 The OAuth 2.0 Protocol: Bearer Tokens draft-ietf-oauth-v2-bearer-00 Abstract This specification describes how to use bearer tokens when accessing OAuth 2.0 protected resources. 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 June 3, 2011. Copyright Notice Copyright (c) 2010 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 Jones, et al. Expires June 3, 2011 [Page 1] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Notational Conventions . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Authenticated Requests . . . . . . . . . . . . . . . . . . . . 4 2.1. The Authorization Request Header Field . . . . . . . . . . 5 2.2. URI Query Parameter . . . . . . . . . . . . . . . . . . . 5 2.3. Form-Encoded Body Parameter . . . . . . . . . . . . . . . 6 2.4. The WWW-Authenticate Response Header Field . . . . . . . . 7 2.5. Error Codes . . . . . . . . . . . . . . . . . . . . . . . 8 3. Security Considerations . . . . . . . . . . . . . . . . . . . 9 3.1. Validate SSL Certificate Chains . . . . . . . . . . . . . 9 3.2. Always use TLS (https) . . . . . . . . . . . . . . . . . . 9 3.3. Don't store bearer tokens in cookies . . . . . . . . . . . 9 3.4. Issue short-lived bearer tokens . . . . . . . . . . . . . 9 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9 Appendix B. Document History . . . . . . . . . . . . . . . . . . 10 4. Normative References . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Jones, et al. Expires June 3, 2011 [Page 2] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 1. Introduction OAuth enables clients to access protected resources by obtaining an access token (a string that denotes a specific scope, duration, and other attributes), rather than using the resource owner's credentials. Tokens are issued to third-party clients by an authorization server with the approval of the resource owner. The client uses the access token to access the protected resources hosted by the resource server. This specification describes how to make protected resource requests by treating an OAuth access token as a bearer token. This specification defines the use of OAuth over HTTP [RFC2616] (or HTTP over TLS as defined by [RFC2818]). Other specifications may extend it for use with other transport protocols. 1.1. Notational 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 [RFC2119]. This document uses the Augmented Backus-Naur Form (ABNF) notation of [I-D.ietf-httpbis-p1-messaging]. Additionally, the following rules are included from [RFC2617]: realm, auth-param; from [RFC3986]: URI- Reference; and from [I-D.ietf-httpbis-p1-messaging]: OWS, RWS, and quoted-string. Unless otherwise noted, all the protocol parameter names and values are case sensitive. 1.2. Terminology All terms are as defined in The OAuth 2.0 Protocol [OAuth2]. 1.3. Overview OAuth provides a method for clients to access a protected resource on behalf of a resource owner. Before a client can access a protected resource, it must first obtain authorization (access grant) from the resource owner, then exchange the access grant for an access token (representing the grant's scope, duration, and other attributes). The client accesses the protected resource by presenting the access token to the resource server. The access token provides an abstraction layer, replacing different authorization constructs (e.g. username and password, assertion) for Jones, et al. Expires June 3, 2011 [Page 3] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 a single token understood by the resource server. This abstraction enables issuing access tokens valid for a short time period, as well as removing the resource server's need to understand a wide range of authentication schemes. +--------+ +---------------+ | |--(A)- Authorization Request ->| Resource | | | | Owner | | |<-(B)----- Access Grant -------| | | | +---------------+ | | | | Access Grant & +---------------+ | |--(C)--- Client Credentials -->| Authorization | | Client | | Server | | |<-(D)----- Access Token -------| | | | +---------------+ | | | | +---------------+ | |--(E)----- Access Token ------>| Resource | | | | Server | | |<-(F)--- Protected Resource ---| | +--------+ +---------------+ Figure 1: Abstract Protocol Flow The abstract flow illustrated in Figure 1 describes the overall OAuth 2.0 protocol architecture. The following steps are specified within this document: E) The client makes a protected resource request to the resource server by presenting the access token. F) The resource server validates the access token, and if valid, serves the request. 2. Authenticated Requests Clients make authenticated token requests using the "Authorization" request header field. Resource servers MUST accept authenticated requests using the "OAuth" HTTP authentication scheme as described in Section 2.1, and MAY support additional methods. Alternatively, clients MAY attempt to include the access token using the HTTP request URI in the query component as described in Section 2.2, or in the HTTP body when using the "application/x-www-form-urlencoded" content type as described in Section 2.3. Resource server MAY support these alternative methods. Jones, et al. Expires June 3, 2011 [Page 4] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 Clients SHOULD only use the request URI or body when the "Authorization" request header field is not available, and MUST NOT use more than one method in each request. 2.1. The Authorization Request Header Field The "Authorization" request header field is used by clients to make authenticated token requests. The client uses the "OAuth" authentication scheme to include the access token in the request. For example: GET /resource HTTP/1.1 Host: server.example.com Authorization: OAuth vF9dft4qmT The "Authorization" header field uses the framework defined by [RFC2617] as follows: credentials = "OAuth" RWS access-token [ RWS 1#auth-param ] access-token = 1*( quoted-char / <"> ) quoted-char = "!" / "#" / "$" / "%" / "&" / "'" / "(" / ")" / "*" / "+" / "-" / "." / "/" / DIGIT / ":" / "<" / "=" / ">" / "?" / "@" / ALPHA / "[" / "]" / "^" / "_" / "`" / "{" / "|" / "}" / "~" / "\" / "," / ";" NOTE: [RFC5849] defines a different format for the "OAuth" authentication scheme. Resource servers can differentiate between the two protocol versions based on the presence of the "oauth_signature_method" which is REQUIRED in the previous version and is not supported by this specification. 2.2. URI Query Parameter When including the access token in the HTTP request URI, the client adds the access token to the request URI query component as defined by [RFC3986] using the "oauth_token" parameter. For example, the client makes the following HTTP request using transport-layer security: GET /resource?oauth_token=vF9dft4qmT HTTP/1.1 Host: server.example.com The HTTP request URI query can include other request-specific parameters, in which case, the "oauth_token" parameters SHOULD be Jones, et al. Expires June 3, 2011 [Page 5] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 appended following the request-specific parameters, properly separated by an "&" character (ASCII code 38). For example: http://example.com/resource?x=y&oauth_token=vF9dft4qmT NOTE: The "oauth_token" parameter is used by the previous version of the OAuth protocol as described in [RFC5849]. Resource servers can differentiate between the two protocol versions based on the presence of the "oauth_signature_method" which is REQUIRED in the previous version and is not supported by this specification. 2.3. Form-Encoded Body Parameter When including the access token in the HTTP request entity-body, the client adds the access token to the request body using the "oauth_token" parameter. The client can use this method only if the following REQUIRED conditions are met: o The entity-body is single-part. o The entity-body follows the encoding requirements of the "application/x-www-form-urlencoded" content-type as defined by [W3C.REC-html401-19991224]. o The HTTP request entity-header includes the "Content-Type" header field set to "application/x-www-form-urlencoded". o The HTTP request method is "POST", "PUT", or "DELETE". The entity-body can include other request-specific parameters, in which case, the "oauth_token" parameters SHOULD be appended following the request-specific parameters, properly separated by an "&" character (ASCII code 38). For example, the client makes the following HTTP request using transport-layer security: POST /resource HTTP/1.1 Host: server.example.com Content-Type: application/x-www-form-urlencoded oauth_token=vF9dft4qmT NOTE: The "oauth_token" parameter is used by the previous version of the OAuth protocol as described in [RFC5849]. Resource servers can differentiate between the two protocol versions based on the Jones, et al. Expires June 3, 2011 [Page 6] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 presence of the "oauth_signature_method" which is REQUIRED in the previous version and is not supported by this specification. 2.4. The WWW-Authenticate Response Header Field If the protected resource request contains an invalid access token or is malformed, the resource server MUST include the HTTP "WWW-Authenticate" response header field. The "WWW-Authenticate" header field uses the framework defined by [RFC2617] as follows: challenge = "OAuth" RWS token-challenge token-challenge = realm [ CS error ] [ CS error-desc ] [ CS error-uri ] [ CS scope ] [ CS 1#auth-param ] error = "error" "=" <"> token <"> error-desc = "error_description" "=" quoted-string error-uri = "error_uri" = <"> URI-Reference <"> scope = quoted-value / <"> quoted-value *( 1*SP quoted-value ) <"> quoted-value = 1*quoted-char CS = OWS "," OWS For example: HTTP/1.1 401 Unauthorized WWW-Authenticate: OAuth realm="Example Service", error="invalid_token", error_description="The access token expired" The "realm" attribute is used to provide the protected resources partition as defined by [RFC2617]. [[ add explanation ]] The "error" attribute is used to provide the client with the reason why the access request was declined. The parameter values are described in Section 2.5. The "error_description" attribute provides a human-readable text containing additional information, used to assist in the understanding and resolution of the error occurred. The "error_uri" attribute provides a URI identifying a human-readable web page with information about the error, used to offer the end-user Jones, et al. Expires June 3, 2011 [Page 7] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 with additional information about the error. If the value is not an absolute URI, it is relative to the URI of the requested protected resource. The "scope" attribute is a space-delimited list of scope values indicating the required scope of the access token for accessing the requested resource. 2.5. Error Codes When a request fails, the resource server responds using the appropriate HTTP status code (typically, 400, 401, or 403), and includes one of the following error codes in the response: invalid_request The request is missing a required parameter, includes an unsupported parameter or parameter value, repeats the same parameter, uses more than one method for including an access token, or is otherwise malformed. The resource server SHOULD respond with the HTTP 400 (Bad Request) status code. invalid_token The access token provided is expired, revoked, malformed, or invalid for other reasons. The resource SHOULD respond with the HTTP 401 (Unauthorized) status code. The client MAY request a new access token and retry the protected resource request. insufficient_scope The request requires higher privileges than provided by the access token. The resource server SHOULD respond with the HTTP 403 (Forbidden) status code and MAY include the "scope" attribute with the scope necessary to access the protected resource. [[ Add mechanism for extending error codes ]] If the request lacks any authentication information (i.e. the client was unaware authentication is necessary or attempted using an unsupported authentication method), the resource server SHOULD not include an error code or other error information. For example: HTTP/1.1 401 Unauthorized WWW-Authenticate: OAuth realm="Example Service" Jones, et al. Expires June 3, 2011 [Page 8] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 3. Security Considerations Implementers and deployers must ensure that bearer tokens are not leaked to unintended parties, as they will be able to use them to gain access to protected resources. This is the primary security consideration when using bearer tokens with OAuth and underlies all the more specific statements that follow. 3.1. Validate SSL Certificate Chains The client must validate the TLS certificate chain when making requests to protected resources. Failing to do so may enable DNS hijacking attacks to steal the token and gain unintended access. 3.2. Always use TLS (https) Clients must always use TLS (https) when making requests with bearer tokens. Failing to do so exposes the token to numerous attacks that could give attackers unintended access. 3.3. Don't store bearer tokens in cookies As cookies are generally sent in the clear, implementations must not store bearer tokens within them. 3.4. Issue short-lived bearer tokens Using short-lived (one hour or less) bearer tokens can reduce the impact of one of them being leaked. The User-Agent flow should only issue short lived access tokens. Appendix A. Acknowledgements The following people contributed to preliminary versions of this document: Blaine Cook (BT), Brian Eaton (Google), Yaron Goland (Microsoft), Brent Goldman (Facebook), Raffi Krikorian (Twitter), Luke Shepard (Facebook), and Allen Tom (Yahoo!). The content and concepts within are a product of the OAuth community, WRAP community, and the OAuth Working Group. The OAuth Working Group has dozens of very active contributors who proposed ideas and wording for this document, including: [[ If your name is missing or you think someone should be added here, please send Mike Jones a note - don't be shy ]] Michael Adams, Andrew Arnott, Dirk Balfanz, Brian Campbell, Leah Culver, Bill de hOra, Brian Ellin, Igor Faynberg, George Fletcher, Jones, et al. Expires June 3, 2011 [Page 9] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 Tim Freeman, Evan Gilbert, Justin Hart, John Kemp, Chasen Le Hara, Michael B. Jones, Torsten Lodderstedt, Eve Maler, James Manger, Laurence Miao, Chuck Mortimore, Justin Richer, Peter Saint-Andre, Nat Sakimura, Rob Sayre, Marius Scurtescu, Naitik Shah, Justin Smith, Jeremy Suriel, Christian Stuebner, Paul Tarjan, and Franklin Tse. Appendix B. Document History [[ to be removed by RFC editor before publication as an RFC ]] -00 o Initial draft based on preliminary version of OAuth 2.0 draft 11. 4. Normative References [I-D.ietf-httpbis-p1-messaging] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., Leach, P., Berners-Lee, T., and J. Reschke, "HTTP/1.1, part 1: URIs, Connections, and Message Parsing", draft-ietf-httpbis-p1-messaging-09 (work in progress), March 2010. [OAuth2] Hammer-Lahav, E., Ed., Recordon, D., and D. Hardt, "The OAuth 2.0 Protocol", 2010. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication: Basic and Digest Access Authentication", RFC 2617, June 1999. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849, April 2010. Jones, et al. Expires June 3, 2011 [Page 10] Internet-Draft OAuth 2.0 Bearer Tokens November 2010 [W3C.REC-html401-19991224] Raggett, D., Hors, A., and I. Jacobs, "HTML 4.01 Specification", World Wide Web Consortium Recommendation REC-html401-19991224, December 1999, . Authors' Addresses Michael B. Jones (editor) Microsoft Email: mbj@microsoft.com URI: http://self-issued.info/ Eran Hammer-Lahav Yahoo! Email: eran@hueniverse.com URI: http://hueniverse.com Dick Hardt independent Email: dick.hardt@gmail.com URI: http://dickhardt.org/ David Recordon Facebook Email: davidrecordon@facebook.com URI: http://www.davidrecordon.com/ Jones, et al. Expires June 3, 2011 [Page 11]