Internet DRAFT - draft-ietf-oauth-v2-bearer
draft-ietf-oauth-v2-bearer
OAuth Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track D. Hardt
Expires: February 2, 2013 independent
August 1, 2012
The OAuth 2.0 Authorization Framework: Bearer Token Usage
draft-ietf-oauth-v2-bearer-23
Abstract
This specification describes how to use bearer tokens in HTTP
requests to access OAuth 2.0 protected resources. Any party in
possession of a bearer token (a "bearer") can use it to get access to
the associated resources (without demonstrating possession of a
cryptographic key). To prevent misuse, bearer tokens need to be
protected from disclosure in storage and in transport.
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 2, 2013.
Copyright Notice
Copyright (c) 2012 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
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publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Authenticated Requests . . . . . . . . . . . . . . . . . . . . 5
2.1. Authorization Request Header Field . . . . . . . . . . . . 5
2.2. Form-Encoded Body Parameter . . . . . . . . . . . . . . . 6
2.3. URI Query Parameter . . . . . . . . . . . . . . . . . . . 7
3. The WWW-Authenticate Response Header Field . . . . . . . . . . 8
3.1. Error Codes . . . . . . . . . . . . . . . . . . . . . . . 9
4. Example Access Token Response . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5.1. Security Threats . . . . . . . . . . . . . . . . . . . . . 11
5.2. Threat Mitigation . . . . . . . . . . . . . . . . . . . . 11
5.3. Summary of Recommendations . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
6.1. OAuth Access Token Type Registration . . . . . . . . . . . 14
6.1.1. The "Bearer" OAuth Access Token Type . . . . . . . . . 14
6.2. OAuth Extensions Error Registration . . . . . . . . . . . 14
6.2.1. The "invalid_request" Error Value . . . . . . . . . . 15
6.2.2. The "invalid_token" Error Value . . . . . . . . . . . 15
6.2.3. The "insufficient_scope" Error Value . . . . . . . . . 15
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Normative References . . . . . . . . . . . . . . . . . . . 16
7.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 17
Appendix B. Document History . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
OAuth enables clients to access protected resources by obtaining an
access token, which is defined in OAuth 2.0 Authorization
[I-D.ietf-oauth-v2] as "a string representing an access authorization
issued to the client", rather than using the resource owner's
credentials directly.
Tokens are issued to 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 when
the OAuth access token is a bearer token.
This specification defines the use of bearer tokens over HTTP/1.1
[RFC2616] using TLS [RFC5246] to access protected resources. TLS is
mandatory to implement and use with this specification; other
specifications may extend this specification for use with other
protocols. While designed for use with access tokens resulting from
OAuth 2.0 Authorization [I-D.ietf-oauth-v2] flows to access OAuth
protected resources, this specification actually defines a general
HTTP authorization method that can be used with bearer tokens from
any source to access any resources protected by those bearer tokens.
The Bearer authentication scheme is intended primarily for server
authentication using the WWW-Authenticate and Authorization HTTP
headers, but does not preclude its use for proxy authentication.
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 Key words for use in
RFCs to Indicate Requirement Levels [RFC2119].
This document uses the Augmented Backus-Naur Form (ABNF) notation of
[RFC5234]. Additionally, the following rules are included from
HTTP/1.1 [RFC2617]: auth-param and auth-scheme; and from Uniform
Resource Identifier (URI) [RFC3986]: URI-Reference.
Unless otherwise noted, all the protocol parameter names and values
are case sensitive.
1.2. Terminology
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Bearer Token
A security token with the property that any party in possession of
the token (a "bearer") can use the token in any way that any other
party in possession of it can. Using a bearer token does not
require a bearer to prove possession of cryptographic key material
(proof-of-possession).
All other terms are as defined in OAuth 2.0 Authorization
[I-D.ietf-oauth-v2].
1.3. Overview
OAuth provides a method for clients to access a protected resource on
behalf of a resource owner. In the general case, before a client can
access a protected resource, it must first obtain an authorization
grant from the resource owner and then exchange the authorization
grant for an access token. The access token represents the grant's
scope, duration, and other attributes granted by the authorization
grant. The client accesses the protected resource by presenting the
access token to the resource server. In some cases, a client can
directly present its own credentials to an authorization server to
obtain an access token without having to first obtain an
authorization grant from a resource owner.
The access token provides an abstraction, replacing different
authorization constructs (e.g., username and password, assertion) for
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.
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+--------+ +---------------+
| |--(A)- Authorization Request ->| Resource |
| | | Owner |
| |<-(B)-- Authorization Grant ---| |
| | +---------------+
| |
| | +---------------+
| |--(C)-- Authorization Grant -->| Authorization |
| Client | | Server |
| |<-(D)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(E)----- Access Token ------>| Resource |
| | | Server |
| |<-(F)--- Protected Resource ---| |
+--------+ +---------------+
Figure 1: Abstract Protocol Flow
The abstract OAuth 2.0 flow illustrated in Figure 1 describes the
interaction between the four roles. The following steps are
specified within this document:
E) The client requests the protected resource from the resource
server and authenticates by presenting the access token.
F) The resource server validates the access token, and if valid,
serves the request.
This document also imposes semantic requirements upon the access
token returned in Step D.
2. Authenticated Requests
This section defines three methods of sending bearer access tokens in
resource requests to resource servers. Clients MUST NOT use more
than one method to transmit the token in each request.
2.1. Authorization Request Header Field
When sending the access token in the "Authorization" request header
field defined by HTTP/1.1 [RFC2617], the client uses the "Bearer"
authentication scheme to transmit the access token.
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For example:
GET /resource HTTP/1.1
Host: server.example.com
Authorization: Bearer mF_9.B5f-4.1JqM
The "Authorization" header field uses the framework defined by
HTTP/1.1 [RFC2617] as follows:
b64token = 1*( ALPHA / DIGIT /
"-" / "." / "_" / "~" / "+" / "/" ) *"="
credentials = "Bearer" 1*SP b64token
Clients SHOULD make authenticated requests with a bearer token using
the "Authorization" request header field with the "Bearer" HTTP
authorization scheme. Resource servers MUST support this method.
2.2. Form-Encoded Body Parameter
When sending the access token in the HTTP request entity-body, the
client adds the access token to the request body using the
"access_token" parameter. The client MUST NOT use this method unless
all of the following conditions are met:
o The HTTP request entity-header includes the "Content-Type" header
field set to "application/x-www-form-urlencoded".
o The entity-body follows the encoding requirements of the
"application/x-www-form-urlencoded" content-type as defined by
HTML 4.01 [W3C.REC-html401-19991224].
o The HTTP request entity-body is single-part.
o The content to be encoded in the entity-body MUST consist entirely
of ASCII [USASCII] characters.
o The HTTP request method is one for which the request body has
defined semantics. In particular, this means that the "GET"
method MUST NOT be used.
The entity-body MAY include other request-specific parameters, in
which case, the "access_token" parameter MUST be properly separated
from the request-specific parameters using "&" character(s) (ASCII
code 38).
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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
access_token=mF_9.B5f-4.1JqM
The "application/x-www-form-urlencoded" method SHOULD NOT be used
except in application contexts where participating browsers do not
have access to the "Authorization" request header field. Resource
servers MAY support this method.
2.3. URI Query Parameter
When sending the access token in the HTTP request URI, the client
adds the access token to the request URI query component as defined
by Uniform Resource Identifier (URI) [RFC3986] using the
"access_token" parameter.
For example, the client makes the following HTTP request using
transport-layer security:
GET /resource?access_token=mF_9.B5f-4.1JqM HTTP/1.1
Host: server.example.com
The HTTP request URI query can include other request-specific
parameters, in which case, the "access_token" parameter MUST be
properly separated from the request-specific parameters using "&"
character(s) (ASCII code 38).
For example:
https://server.example.com/resource?access_token=mF_9.B5f-4.1JqM&p=q
Clients using the URI Query Parameter method SHOULD also send a
Cache-Control header containing the "no-store" option. Server
success (2XX status) responses to these requests SHOULD contain a
Cache-Control header with the "private" option.
Because of the security weaknesses associated with the URI method
(see Section 5), including the high likelihood that the URL
containing the access token will be logged, it SHOULD NOT be used
unless it is impossible to transport the access token in the
"Authorization" request header field or the HTTP request entity-body.
Resource servers MAY support this method.
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This method is included to document current use; its use is not
recommended, both due to its security deficiencies (see Section 5)
and because it uses a reserved query parameter name, which is counter
to URI namespace best practices, per the Architecture of the World
Wide Web [W3C.REC-webarch-20041215].
3. The WWW-Authenticate Response Header Field
If the protected resource request does not include authentication
credentials or does not contain an access token that enables access
to the protected resource, the resource server MUST include the HTTP
"WWW-Authenticate" response header field; it MAY include it in
response to other conditions as well. The "WWW-Authenticate" header
field uses the framework defined by HTTP/1.1 [RFC2617].
All challenges defined by this specification MUST use the auth-scheme
value "Bearer". This scheme MUST be followed by one or more auth-
param values. The auth-param attributes used or defined by this
specification are as follows. Other auth-param attributes MAY be
used as well.
A "realm" attribute MAY be included to indicate the scope of
protection in the manner described in HTTP/1.1 [RFC2617]. The
"realm" attribute MUST NOT appear more than once.
The "scope" attribute is defined in Section 3.3 of OAuth 2.0
Authorization [I-D.ietf-oauth-v2]. The "scope" attribute is a space-
delimited list of case sensitive scope values indicating the required
scope of the access token for accessing the requested resource.
"scope" values are implementation defined; there is no centralized
registry for them; allowed values are defined by the authorization
server. The order of "scope" values is not significant. In some
cases, the "scope" value will be used when requesting a new access
token with sufficient scope of access to utilize the protected
resource. Use of the "scope" attribute is OPTIONAL. The "scope"
attribute MUST NOT appear more than once. The "scope" value is
intended for programmatic use and is not meant to be displayed to end
users.
Two example scope values follow; these are taken from the OpenID
Connect [OpenID.Messages] and OATC Online Multimedia Authorization
Protocol [OMAP] OAuth 2.0 use cases, respectively:
scope="openid profile email"
scope="urn:example:channel=HBO&urn:example:rating=G,PG-13"
If the protected resource request included an access token and failed
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authentication, the resource server SHOULD include the "error"
attribute to provide the client with the reason why the access
request was declined. The parameter value is described in
Section 3.1. In addition, the resource server MAY include the
"error_description" attribute to provide developers a human-readable
explanation that is not meant to be displayed to end users. It also
MAY include the "error_uri" attribute with an absolute URI
identifying a human-readable web page explaining the error. The
"error", "error_description", and "error_uri" attributes MUST NOT
appear more than once.
Values for the "scope" attribute MUST NOT include characters outside
the set %x21 / %x23-5B / %x5D-7E specified in Section A.4 of OAuth
2.0 Authorization [I-D.ietf-oauth-v2] for representing scope values
and %x20 for delimiters between scope values. Values for the "error"
and "error_description" attributes MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E specified in Sections A.7
and A.8 of OAuth 2.0 Authorization. Values for the "error_uri"
attribute MUST conform to the URI-Reference syntax, and thus MUST NOT
include characters outside the set %x21 / %x23-5B / %x5D-7E specified
in Section A.9 of OAuth 2.0 Authorization.
For example, in response to a protected resource request without
authentication:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer realm="example"
And in response to a protected resource request with an
authentication attempt using an expired access token:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer realm="example",
error="invalid_token",
error_description="The access token expired"
3.1. Error Codes
When a request fails, the resource server responds using the
appropriate HTTP status code (typically, 400, 401, 403, or 405), 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.
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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.
If the request lacks any authentication information (e.g., 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: Bearer realm="example"
4. Example Access Token Response
Typically a bearer token is returned to the client as part of an
OAuth 2.0 [I-D.ietf-oauth-v2] access token response. An example of
such a response is:
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"access_token":"mF_9.B5f-4.1JqM",
"token_type":"Bearer",
"expires_in":3600,
"refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA"
}
5. Security Considerations
This section describes the relevant security threats regarding token
handling when using bearer tokens and describes how to mitigate these
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threats.
5.1. Security Threats
The following list presents several common threats against protocols
utilizing some form of tokens. This list of threats is based on NIST
Special Publication 800-63 [NIST800-63]. Since this document builds
on the OAuth 2.0 Authorization specification, we exclude a discussion
of threats that are described there or in related documents.
Token manufacture/modification: An attacker may generate a bogus
token or modify the token contents (such as the authentication or
attribute statements) of an existing token, causing the resource
server to grant inappropriate access to the client. For example,
an attacker may modify the token to extend the validity period; a
malicious client may modify the assertion to gain access to
information that they should not be able to view.
Token disclosure: Tokens may contain authentication and attribute
statements that include sensitive information.
Token redirect: An attacker uses a token generated for consumption
by one resource server to gain access to a different resource
server that mistakenly believes the token to be for it.
Token replay: An attacker attempts to use a token that has already
been used with that resource server in the past.
5.2. Threat Mitigation
A large range of threats can be mitigated by protecting the contents
of the token by using a digital signature or a Message Authentication
Code (MAC). Alternatively, a bearer token can contain a reference to
authorization information, rather than encoding the information
directly. Such references MUST be infeasible for an attacker to
guess; using a reference may require an extra interaction between a
server and the token issuer to resolve the reference to the
authorization information. The mechanics of such an interaction are
not defined by this specification.
This document does not specify the encoding or the contents of the
token; hence detailed recommendations about the means of guaranteeing
token integrity protection are outside the scope of this document.
The token integrity protection MUST be sufficient to prevent the
token from being modified.
To deal with token redirect, it is important for the authorization
server to include the identity of the intended recipients (the
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audience), typically a single resource server (or a list of resource
servers), in the token. Restricting the use of the token to a
specific scope is also RECOMMENDED.
The authorization server MUST implement TLS. Which version(s) ought
to be implemented will vary over time, and depend on the widespread
deployment and known security vulnerabilities at the time of
implementation. At the time of this writing, TLS version 1.2
[RFC5246] is the most recent version, but has very limited actual
deployment, and might not be readily available in implementation
toolkits. TLS version 1.0 [RFC2246] is the most widely deployed
version, and will give the broadest interoperability.
To protect against token disclosure, confidentiality protection MUST
be applied using TLS [RFC5246] with a ciphersuite that provides
confidentiality and integrity protection. This requires that the
communication interaction between the client and the authorization
server, as well as the interaction between the client and the
resource server, utilize confidentiality and integrity protection.
Since TLS is mandatory to implement and to use with this
specification, it is the preferred approach for preventing token
disclosure via the communication channel. For those cases where the
client is prevented from observing the contents of the token, token
encryption MUST be applied in addition to the usage of TLS
protection. As a further defense against token disclosure, the
client MUST validate the TLS certificate chain when making requests
to protected resources, including checking the Certificate Revocation
List (CRL) [RFC5280].
Cookies are typically transmitted in the clear. Thus, any
information contained in them is at risk of disclosure. Therefore,
bearer tokens MUST NOT be stored in cookies that can be sent in the
clear. See HTTP State Management Mechanism [RFC6265] for security
considerations about cookies.
In some deployments, including those utilizing load balancers, the
TLS connection to the resource server terminates prior to the actual
server that provides the resource. This could leave the token
unprotected between the front end server where the TLS connection
terminates and the back end server that provides the resource. In
such deployments, sufficient measures MUST be employed to ensure
confidentiality of the token between the front end and back end
servers; encryption of the token is one possible such measure.
To deal with token capture and replay, the following recommendations
are made: First, the lifetime of the token MUST be limited; one means
of achieving this is by putting a validity time field inside the
protected part of the token. Note that using short-lived (one hour
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or less) tokens reduces the impact of them being leaked. Second,
confidentiality protection of the exchanges between the client and
the authorization server and between the client and the resource
server MUST be applied. As a consequence, no eavesdropper along the
communication path is able to observe the token exchange.
Consequently, such an on-path adversary cannot replay the token.
Furthermore, when presenting the token to a resource server, the
client MUST verify the identity of that resource server, as per
Section 3.1 of HTTP Over TLS [RFC2818]. Note that the client MUST
validate the TLS certificate chain when making these requests to
protected resources. Presenting the token to an unauthenticated and
unauthorized resource server or failing to validate the certificate
chain will allow adversaries to steal the token and gain unauthorized
access to protected resources.
5.3. Summary of Recommendations
Safeguard bearer tokens: Client implementations 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 and
underlies all the more specific recommendations that follow.
Validate TLS 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.
Always use TLS (https): Clients MUST always use TLS [RFC5246]
(https) or equivalent transport security when making requests with
bearer tokens. Failing to do so exposes the token to numerous
attacks that could give attackers unintended access.
Don't store bearer tokens in cookies: Implementations MUST NOT store
bearer tokens within cookies that can be sent in the clear (which
is the default transmission mode for cookies). Implementations
that do store bearer tokens in cookies MUST take precautions
against cross site request forgery.
Issue short-lived bearer tokens: Token servers SHOULD issue short-
lived (one hour or less) bearer tokens, particularly when issuing
tokens to clients that run within a web browser or other
environments where information leakage may occur. Using short-
lived bearer tokens can reduce the impact of them being leaked.
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Issue scoped bearer tokens: Token servers SHOULD issue bearer tokens
that contain an audience restriction, scoping their use to the
intended relying party or set of relying parties.
Don't pass bearer tokens in page URLs: Bearer tokens SHOULD NOT be
passed in page URLs (for example as query string parameters).
Instead, bearer tokens SHOULD be passed in HTTP message headers or
message bodies for which confidentiality measures are taken.
Browsers, web servers, and other software may not adequately
secure URLs in the browser history, web server logs, and other
data structures. If bearer tokens are passed in page URLs,
attackers might be able to steal them from the history data, logs,
or other unsecured locations.
6. IANA Considerations
6.1. OAuth Access Token Type Registration
This specification registers the following access token type in the
OAuth Access Token Type Registry defined in OAuth 2.0 Authorization
[I-D.ietf-oauth-v2].
6.1.1. The "Bearer" OAuth Access Token Type
Type name:
Bearer
Additional Token Endpoint Response Parameters:
(none)
HTTP Authentication Scheme(s):
Bearer
Change controller:
IETF
Specification document(s):
[[ this document ]]
6.2. OAuth Extensions Error Registration
This specification registers the following error values in the OAuth
Extensions Error Registry defined in OAuth 2.0 Authorization
[I-D.ietf-oauth-v2].
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6.2.1. The "invalid_request" Error Value
Error name:
invalid_request
Error usage location:
Resource access error response
Related protocol extension:
Bearer access token type
Change controller:
IETF
Specification document(s):
[[ this document ]]
6.2.2. The "invalid_token" Error Value
Error name:
invalid_token
Error usage location:
Resource access error response
Related protocol extension:
Bearer access token type
Change controller:
IETF
Specification document(s):
[[ this document ]]
6.2.3. The "insufficient_scope" Error Value
Error name:
insufficient_scope
Error usage location:
Resource access error response
Related protocol extension:
Bearer access token type
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Change controller:
IETF
Specification document(s):
[[ this document ]]
7. References
7.1. Normative References
[I-D.ietf-oauth-v2]
Hardt, D., "The OAuth 2.0 Authorization Framework",
draft-ietf-oauth-v2-31 (work in progress), July 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
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April 2011.
[USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
[W3C.REC-html401-19991224]
Hors, A., Raggett, D., and I. Jacobs, "HTML 4.01
Specification", World Wide Web Consortium
Recommendation REC-html401-19991224, December 1999,
<http://www.w3.org/TR/1999/REC-html401-19991224>.
[W3C.REC-webarch-20041215]
Jacobs, I. and N. Walsh, "Architecture of the World Wide
Web, Volume One", World Wide Web Consortium
Recommendation REC-webarch-20041215, December 2004,
<http://www.w3.org/TR/2004/REC-webarch-20041215>.
7.2. Informative References
[NIST800-63]
Burr, W., Dodson, D., Perlner, R., Polk, T., Gupta, S.,
and E. Nabbus, "NIST Special Publication 800-63-1,
INFORMATION SECURITY", December 2008.
[OMAP] Huff, J., Schlacht, D., Nadalin, A., Simmons, J.,
Rosenberg, P., Madsen, P., Ace, T., Rickelton-Abdi, C.,
and B. Boyer, "Online Multimedia Authorization Protocol:
An Industry Standard for Authorized Access to Internet
Multimedia Resources", April 2012.
[OpenID.Messages]
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B.,
Mortimore, C., and E. Jay, "OpenID Connect Messages 1.0",
June 2012.
Appendix A. Acknowledgements
The following people contributed to preliminary versions of this
document: Blaine Cook (BT), Brian Eaton (Google), Yaron Y. 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, the WRAP
community, and the OAuth Working Group. David Recordon created a
preliminary draft of this specification based upon a preliminary
version of OAuth 2.0 draft 11. Michael B. Jones created draft 00 of
this specification using portions of David's preliminary draft, and
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edited all subsequent versions.
The OAuth Working Group has dozens of very active contributors who
proposed ideas and wording for this document, including: Michael
Adams, Amanda Anganes, Andrew Arnott, Derek Atkins, Dirk Balfanz,
John Bradley, Brian Campbell, Francisco Corella, Leah Culver, Bill de
hOra, Breno de Medeiros, Brian Ellin, Stephen Farrell, Igor Faynberg,
George Fletcher, Tim Freeman, Evan Gilbert, Yaron Y. Goland, Thomas
Hardjono, Justin Hart, Phil Hunt, John Kemp, Eran Hammer, Chasen Le
Hara, Dick Hardt, Barry Leiba, Amos Jeffries, Michael B. Jones,
Torsten Lodderstedt, Paul Madsen, Eve Maler, James Manger, Laurence
Miao, William J. Mills, Chuck Mortimore, Anthony Nadalin, Axel
Nennker, Mark Nottingham, David Recordon, Julian Reschke, Rob
Richards, Justin Richer, Peter Saint-Andre, Nat Sakimura, Rob Sayre,
Marius Scurtescu, Naitik Shah, Justin Smith, Jeremy Suriel, Christian
Stuebner, Doug Tangren, Paul Tarjan, Hannes Tschofenig, Franklin Tse,
Sean Turner, Paul Walker, Shane Weeden, Skylar Woodward, and Zachary
Zeltsan.
Appendix B. Document History
[[ to be removed by the RFC editor before publication as an RFC ]]
-23
o Removed David Recordon's name from the author list, at his
request.
-22
o Removed uses of HTTPbis in favor of RFC 2616 and RFC 2617, since
HTTPbis is not an approved standard.
o Match formatting of artwork elements with OAuth core
specification.
-21
o Changed "NOT RECOMMENDED" to "not recommended" in caveat about the
URI Query Parameter method.
o Changed "other specifications may extend this specification for
use with other transport protocols" to "other specifications may
extend this specification for use with other protocols".
o Changed Acknowledgements to use only ASCII characters, per the RFC
style guide.
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-20
o Added caveat about using a reserved query parameter name being
counter to URI namespace best practices.
o Specified use of Cache-Control options when using the URI Query
Parameter method.
o Changed title to "The OAuth 2.0 Authorization Framework: Bearer
Token Usage".
o Referenced syntax definitions for the "scope", "error",
"error_description", and "error_uri" parameters in the OAuth 2.0
core spec.
o Registered the "invalid_request", "invalid_token", and
"insufficient_scope" error values in the OAuth Extensions Error
Registry.
o Acknowledged additional individuals.
-19
o Addressed DISCUSS issues and comments raised for which resolutions
have been agreed to. No normative changes were made. Changes
made were:
o Use ABNF from RFC 5234.
o Added sentence "The Bearer authentication scheme is intended
primarily for server authentication using the WWW-Authenticate and
Authorization HTTP headers, but does not preclude its use for
proxy authentication" to the introduction.
o In the introduction, state that this document also imposes
semantic requirements upon the access token.
o Reference the "scope" definition in the OAuth core spec.
o Added "scope" examples.
o Reference RFC 6265 for security considerations about cookies.
-18
o Changed example bearer token value from vF9dft4qmT to mF_9.B5f-
4.1JqM.
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o Added example access token response returning a Bearer token.
-17
o Restore RFC 2818 reference for server identity verification and
add RFC 5280 reference for certificate revocation lists, per Gen-
ART review comments.
-16
o Use the HTTPbis auth-param syntax for Bearer challenge attributes.
o Dropped the sentence "The "realm" value is intended for
programmatic use and is not meant to be displayed to end users".
o Reordered form-encoded body parameter description bullets for
better readability.
o Added [USASCII] reference.
-15
o Clarified that form-encoded content must consist entirely of ASCII
characters.
o Added TLS version requirements.
o Applied editorial improvements suggested by Mark Nottingham during
the APPS area review.
-14
o Changes made in response to review comments by Security Area
Director Stephen Farrell. Specifically:
o Strengthened warnings about passing an access token as a query
parameter and more precisely described the limitations placed upon
the use of this method.
o Clarified that the "realm" attribute MAY included to indicate the
scope of protection in the manner described in HTTP/1.1, Part 7
[I-D.ietf-httpbis-p7-auth].
o Normatively stated that "the token integrity protection MUST be
sufficient to prevent the token from being modified".
o Added statement that "TLS is mandatory to implement and use with
this specification" to the introduction.
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o Stated that TLS MUST be used with "a ciphersuite that provides
confidentiality and integrity protection".
o Added "As a further defense against token disclosure, the client
MUST validate the TLS certificate chain when making requests to
protected resources" to the Threat Mitigation section.
o Clarified that putting a validity time field inside the protected
part of the token is one means, but not the only means, of
limiting the lifetime of the token.
o Dropped the confusing phrase "for instance, through the use of
TLS" from the sentence about confidentiality protection of the
exchanges.
o Reference RFC 6125 for identity verification, rather than RFC
2818.
o Stated that the token MUST be protected between front end and back
end servers when the TLS connection terminates at a front end
server that is distinct from the actual server that provides the
resource.
o Stated that bearer tokens MUST NOT be stored in cookies that can
be sent in the clear in the Threat Mitigation section.
o Replaced sole remaining reference to [RFC2616] with HTTPbis
[I-D.ietf-httpbis-p1-messaging] reference.
o Replaced all references where the reference is used as if it were
part of the sentence (such as "defined by [I-D.whatever]") with
ones where the specification name is used, followed by the
reference (such as "defined by Whatever [I-D.whatever]").
o Other on-normative editorial improvements.
-13
o At the request of Hannes Tschofenig, made ABNF changes to make it
clear that no special WWW-Authenticate response header field
parsers are needed. The "scope", "error-description", and
"error-uri" parameters are all now defined as quoted-string in the
ABNF (as "error" already was). Restrictions on these values that
were formerly described in the ABNFs are now described in
normative text instead.
-12
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o Made non-normative editorial changes that Hannes Tschofenig
requested be applied prior to forwarding the specification to the
IESG.
o Added rationale for the choice of the b64token syntax.
o Added rationale stating that receivers are free to parse the
"scope" attribute using a standard quoted-string parser, since it
will correctly process all legal "scope" values.
o Added additional active working group contributors to the
Acknowledgements section.
-11
o Replaced uses of <"> with DQUOTE to pass ABNF syntax check.
-10
o Removed the #auth-param option from Authorization header syntax
(leaving only the b64token syntax).
o Restricted the "scope" value character set to %x21 / %x23-5B /
%x5D-7E (printable ASCII characters excluding double-quote and
backslash). Indicated that scope is intended for programmatic use
and is not meant to be displayed to end users.
o Restricted the character set for "error_description" strings to SP
/ VCHAR and indicated that they are not meant to be displayed to
end users.
o Included more description in the Abstract, since Hannes Tschofenig
indicated that the RFC editor would require this.
o Changed "Access Grant" to "Authorization Grant", as was done in
the core spec.
o Simplified the introduction to the Authenticated Requests section.
-09
o Incorporated working group last call comments. Specific changes
were:
o Use definitions from [I-D.ietf-httpbis-p7-auth] rather than
[RFC2617].
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o Update credentials definition to conform to [I-D.ietf-httpbis-p7-
auth].
o Further clarified that query parameters may occur in any order.
o Specify that error_description is UTF-8 encoded (matching the core
specification).
o Registered "Bearer" Authentication Scheme in Authentication Scheme
Registry defined by [I-D.ietf-httpbis-p7-auth].
o Updated references to oauth-v2, httpbis-p1-messaging, and httpbis-
p7-auth drafts.
o Other wording improvements not introducing normative changes.
-08
o Updated references to oauth-v2 and HTTPbis drafts.
-07
o Added missing comma in error response example.
-06
o Changed parameter name "bearer_token" to "access_token", per
working group consensus.
o Changed HTTP status code for "invalid_request" error code from
HTTP 401 (Unauthorized) back to HTTP 400 (Bad Request), per input
from HTTP working group experts.
-05
o Removed OAuth Errors Registry, per design team input.
o Changed HTTP status code for "invalid_request" error code from
HTTP 400 (Bad Request) to HTTP 401 (Unauthorized) to match HTTP
usage [[ change pending working group consensus ]].
o Added missing quotation marks in error-uri definition.
o Added note to add language and encoding information to
error_description if the core specification does.
o Explicitly reference the Augmented Backus-Naur Form (ABNF) defined
in [RFC5234].
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o Use auth-param instead of repeating its definition, which is (
token "=" ( token / quoted-string ) ).
o Clarify security considerations about including an audience
restriction in the token and include a recommendation to issue
scoped bearer tokens in the summary of recommendations.
-04
o Edits responding to working group last call feedback on -03.
Specific edits enumerated below.
o Added Bearer Token definition in Terminology section.
o Changed parameter name "oauth_token" to "bearer_token".
o Added realm parameter to "WWW-Authenticate" response to comply
with [RFC2617].
o Removed "[ RWS 1#auth-param ]" from "credentials" definition since
it did not comply with the ABNF in [I-D.ietf-httpbis-p7-auth].
o Removed restriction that the "bearer_token" (formerly
"oauth_token") parameter be the last parameter in the entity-body
and the HTTP request URI query.
o Do not require WWW-Authenticate Response in a reply to a malformed
request, as an HTTP 400 Bad Request response without a WWW-
Authenticate header is likely the right response in some cases of
malformed requests.
o Removed OAuth Parameters registry extension.
o Numerous editorial improvements suggested by working group
members.
-03
o Restored the WWW-Authenticate response header functionality
deleted from the framework specification in draft 12 based upon
the specification text from draft 11.
o Augmented the OAuth Parameters registry by adding two additional
parameter usage locations: "resource request" and "resource
response".
o Registered the "oauth_token" OAuth parameter with usage location
"resource request".
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o Registered the "error" OAuth parameter.
o Created the OAuth Error registry and registered errors.
o Changed the "OAuth2" OAuth access token type name to "Bearer".
-02
o Incorporated feedback received on draft 01. Most changes were to
the security considerations section. No normative changes were
made. Specific changes included:
o Changed terminology from "token reuse" to "token capture and
replay".
o Removed sentence "Encrypting the token contents is another
alternative" from the security considerations since it was
redundant and potentially confusing.
o Corrected some references to "resource server" to be
"authorization server" in the security considerations.
o Generalized security considerations language about obtaining
consent of the resource owner.
o Broadened scope of security considerations description for
recommendation "Don't pass bearer tokens in page URLs".
o Removed unused reference to OAuth 1.0.
o Updated reference to framework specification and updated David
Recordon's e-mail address.
o Removed security considerations text on authenticating clients.
o Registered the "OAuth2" OAuth access token type and "oauth_token"
parameter.
-01
o First public draft, which incorporates feedback received on -00
including enhanced Security Considerations content. This version
is intended to accompany OAuth 2.0 draft 11.
-00
o Initial draft based on preliminary version of OAuth 2.0 draft 11.
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Authors' Addresses
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: http://self-issued.info/
Dick Hardt
independent
Email: dick.hardt@gmail.com
URI: http://dickhardt.org/
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