Network Working Group E. Hammer-Lahav, Ed.
Internet-Draft Yahoo!
Intended status: Standards Track D. Recordon
Expires: November 14, 2010 Facebook
D. Hardt
May 13, 2010
The OAuth 2.0 Protocol
draft-ietf-oauth-v2-05
Abstract
This specification describes the OAuth 2.0 protocol. OAuth provides
a method for making authenticated HTTP requests using a token - an
identifier used to denote an access grant with specific scope,
duration, and other attributes. Tokens are issued to third-party
clients by an authorization server with the approval of the resource
owner. OAuth defines multiple flows for obtaining a token to support
a wide range of client types and user experience.
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 November 14, 2010.
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
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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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.4. Notational Conventions . . . . . . . . . . . . . . . . . . 8
2.5. Conformance . . . . . . . . . . . . . . . . . . . . . . . 8
3. Obtaining an Access Token . . . . . . . . . . . . . . . . . . 9
3.1. Client Credentials . . . . . . . . . . . . . . . . . . . . 9
3.2. End-User Endpoint . . . . . . . . . . . . . . . . . . . . 9
3.3. Token Endpoint . . . . . . . . . . . . . . . . . . . . . . 10
3.3.1. Client Authentication . . . . . . . . . . . . . . . . 11
3.3.2. Response Format . . . . . . . . . . . . . . . . . . . 12
3.4. Flow Parameters . . . . . . . . . . . . . . . . . . . . . 14
3.5. User-Agent Flow . . . . . . . . . . . . . . . . . . . . . 15
3.5.1. Client Requests Authorization . . . . . . . . . . . . 16
3.5.2. Client Extracts Access Token . . . . . . . . . . . . . 19
3.6. Web Server Flow . . . . . . . . . . . . . . . . . . . . . 20
3.6.1. Client Requests Authorization . . . . . . . . . . . . 21
3.6.2. Client Requests Access Token . . . . . . . . . . . . . 24
3.7. Device Flow . . . . . . . . . . . . . . . . . . . . . . . 25
3.7.1. Client Requests Authorization . . . . . . . . . . . . 27
3.7.2. Client Requests Access Token . . . . . . . . . . . . . 29
3.8. Username and Password Flow . . . . . . . . . . . . . . . . 31
3.8.1. Client Requests Access Token . . . . . . . . . . . . . 33
3.9. Client Credentials Flow . . . . . . . . . . . . . . . . . 35
3.9.1. Client Requests Access Token . . . . . . . . . . . . . 35
3.10. Assertion Flow . . . . . . . . . . . . . . . . . . . . . . 37
3.10.1. Client Requests Access Token . . . . . . . . . . . . . 38
4. Refreshing an Access Token . . . . . . . . . . . . . . . . . . 40
5. Accessing a Protected Resource . . . . . . . . . . . . . . . . 42
5.1. The Authorization Request Header . . . . . . . . . . . . . 43
5.2. Bearer Token Requests . . . . . . . . . . . . . . . . . . 44
5.2.1. URI Query Parameter . . . . . . . . . . . . . . . . . 45
5.2.2. Form-Encoded Body Parameter . . . . . . . . . . . . . 45
5.3. Cryptographic Tokens Requests . . . . . . . . . . . . . . 46
5.3.1. The 'hmac-sha256' Algorithm . . . . . . . . . . . . . 47
6. Identifying a Protected Resource . . . . . . . . . . . . . . . 50
6.1. The WWW-Authenticate Response Header . . . . . . . . . . . 50
7. Security Considerations . . . . . . . . . . . . . . . . . . . 51
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8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 52
Appendix A. Differences from OAuth 1.0a . . . . . . . . . . . . . 52
Appendix B. Document History . . . . . . . . . . . . . . . . . . 52
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 53
10.1. Normative References . . . . . . . . . . . . . . . . . . . 53
10.2. Informative References . . . . . . . . . . . . . . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 55
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1. Authors
This specification was authored with the participation and based on
the work of Allen Tom (Yahoo!), Brian Eaton (Google), Brent Goldman
(Facebook), Luke Shepard (Facebook), Raffi Krikorian (Twitter), and
Yaron Goland (Microsoft).
2. Introduction
With the increasing use of distributed web services and cloud
computing, third-party applications require access to server-hosted
resources. These resources are usually protected and require
authentication using the resource owner's credentials (typically a
username and password). In the traditional client-server
authentication model, a client accessing a protected resource on a
server presents the resource owner's credentials in order to
authenticate and gain access.
Resource owners should not be required to share their credentials
when granting third-party applications access to their protected
resources. They should also have the ability to restrict access to a
limited subset of the resources they control, to limit access
duration, or to limit access to the HTTP methods supported by these
resources.
OAuth provides a method for making authenticated HTTP requests using
a token - an identifier used to denote an access grant with specific
scope, duration, and other attributes. Tokens are issued to third-
party clients by an authorization server with the approval of the
resource owner. Instead of sharing their credentials with the
client, resource owners grant access by authenticating directly with
the authorization server which in turn issues a token to the client.
The client uses the token (and optional secret) to authenticate with
the resource server and gain access.
For example, a web user (resource owner) can grant a printing service
(client) access to her protected photos stored at a photo sharing
service (resource server), without sharing her username and password
with the printing service. Instead, she authenticates directly with
the photo sharing service (authorization server) which issues the
printing service delegation-specific credentials (token).
This specification defines the use of OAuth over HTTP [RFC2616] (or
HTTP over TLS 1.0 as defined by [RFC2818]. Other specifications may
extend it for use with other transport protocols.
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2.1. Terminology
resource server
An HTTP [RFC2616] server capable of accepting authenticated
resource requests using the OAuth protocol.
protected resource
An access-restricted resource which can be obtained from a
resource server using an OAuth-authenticated request.
client
An HTTP client capable of making authenticated requests for
protected resources using the OAuth protocol.
resource owner
An entity capable of granting access to a protected resource.
end-user
A human resource owner.
access token
A unique identifier used by the client to make authenticated
requests on behalf of the resource owner. Access tokens may
have a matching secret.
bearer token An access token without a matching secret, used to
obtain access to a protected resource by simply presenting the
access token as-is to the resource server.
authorization server
An HTTP server capable of issuing tokens after successfully
authenticating the resource owner and obtaining authorization.
The authorization server may be the same server as the resource
server, or a separate entity.
end-user endpoint
The authorization server's HTTP endpoint capable of
authenticating the end-user and obtaining authorization.
token endpoint
The authorization server's HTTP endpoint capable of issuing
tokens and refreshing expired tokens.
client identifier
An unique identifier issued to the client to identify itself to
the authorization server. Client identifiers may have a
matching secret.
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refresh token
A unique identifier used by the client to replace an expired
access token with a new access token without having to involve
the resource owner. A refresh token is used when the access
token is valid for a shorter time period than the duration of
the access grant approved by the resource owner.
2.2. Overview
Clients interact with a protected resource, first by requesting
access (which is granted in the form of an access token) from the
authorization server, and then by authenticating with the resource
server by presenting the access token. Figure 1 demonstrates the
flow between the client and authorization server (A, B), and the flow
between the client and resource server (C, D), when the client is
acting autonomously (the client is also the resource owner).
+--------+ +---------------+
| |--(A)------ Credentials --------->| Authorization |
| | | Server |
| |<-(B)------ Access Token ---------| |
| | (w/ Optional Refresh Token) +---------------+
| Client |
| | HTTP Request +---------------+
| |--(C)--- with Access Token ------>| Resource |
| | | Server |
| |<-(D)------ HTTP Response --------| |
+--------+ +---------------+
Figure 1
Access token strings can use any internal structure agreed upon
between the authorization server and the resource server, but their
structure is opaque to the client. Since the access token provides
the client access to the protected resource for the life of the
access token (or until revoked), the authorization server should
issue access tokens which expire within an appropriate time, usually
much shorter than the duration of the access grant.
When an access token expires, the client can request a new access
token from the authorization server by presenting its credentials
again (Figure 1), or by using the refresh token (if issued with the
access token) as shown in Figure 2. Once an expired access token has
been replaced with a new access token (A, B), the client uses the new
access token as before (C, D).
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+--------+ +---------------+
| |--(A)------ Refresh Token ------->| Authorization |
| | | Server |
| |<-(B)------ Access Token ---------| |
| | (with Optional Secret) +---------------+
| Client |
| | HTTP Request +---------------+
| |--(C)--- with Access Token ------>| Resource |
| | | Server |
| |<-(D)----- HTTP Response ---------| |
+--------+ +---------------+
Figure 2
This specification defines a number of authorization flows to support
different client types and scenarios. These authorization flows can
be separated into three groups: user delegation flows, direct
credentials flows, and autonomous flows.
Additional authorization flows may be defined by other specifications
to cover different scenarios and client types.
User delegation flows are used to grant client access to protected
resources by the end-user without sharing the end-user credentials
(e.g. a username and password) with the client. Instead, the end-
user authenticates directly with the authorization server, and grants
client access to its protected resources. The user delegation flows
defined by this specifications are:
o User-Agent Flow - This flow is designed for clients running inside
a user-agent (typically a web browser). This flow is described in
Section 3.5.
o Web Server Flow - This flow is optimized for clients that are part
of a web server application, accessible via HTTP requests. This
flow is described in Section 3.6.
o Device Flow - This flow is suitable for clients executing on
limited devices, but where the end-user has separate access to a
user-agent on another computer or device. This flow is described
in Section 3.7.
Direct credentials flows enable clients to obtain an access token
with a single request using the client credentials or end-user
credentials without seeking additional resource owner authorization.
The direct credentials flows defined by this specification are:
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o Username and Password Flow - This flow is used in cases where the
end-user trusts the client to handle its credentials but it is
still undesirable for the client to store the end-user's username
and password. This flow is only suitable when there is a high
degree of trust between the end-user and the client. This flow is
described in Section 3.8.
o Client Credentials Flow - The client uses its credentials to
obtain an access token. This flow is described in Section 3.9.
Autonomous flows enable clients to use utilize existing trust
relationships or different authorization constructs to obtain an
access token. They provide a bridge between OAuth and other trust
frameworks. The autonomous authorization flow defined by this
specifications is:
o Assertion Flow - The client presents an assertion such as a SAML
[OASIS.saml-core-2.0-os] assertion to the authorization server in
exchange for an access token. This flow is described in
Section 3.10.
2.3. Example
[[ Todo ]]
2.4. 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 realm and auth-
param rules are included from [RFC2617], and the URI-Reference rule
from [RFC3986].
2.5. Conformance
An implementation is not compliant if it fails to satisfy one or more
of the MUST or REQUIRED level requirements for the flows it
implements. An implementation that satisfies all the MUST or
REQUIRED level and all the SHOULD level requirements for its flows is
said to be "unconditionally compliant"; one that satisfies all the
MUST level requirements but not all the SHOULD level requirements for
its flows is said to be "conditionally compliant."
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3. Obtaining an Access Token
The client obtains an access token by using one of the authorization
flows supported by the authorization server. The authorization flows
all use the same authorization and token endpoints, each with a
different set of request parameters and values.
Access tokens have a scope, duration, and other access attributes
granted by the resource owner. These attributes MUST be enforced by
the resource server when receiving a protected resource request, and
by the authorization server when receiving a token refresh request.
In many cases it is desirable to issue access tokens with a shorter
lifetime than the duration of the authorization grant. However, it
may be undesirable to require the resource owner to authorize the
request again. Instead, the authorization server issues a refresh
token in addition to the access token. When the access token
expires, the client can request a new access token without involving
the resource owner as long as the authorization grant is still valid.
The token refresh method is described in Section 4.
3.1. Client Credentials
When requesting access from the authorization server, the client
identifies itself using a set of client credentials. The client
credentials include a client identifier and an OPTIONAL symmetric
shared secret. The means through which the client obtains these
credentials are beyond the scope of this specification, but usually
involve registration with the authorization server.
The client identifier is used by the authorization server to
establish the identity of the client for the purpose of presenting
information to the resource owner prior to granting access, as well
as for providing different service levels to different clients. They
can also be used to block unauthorized clients from requesting
access.
Due to the nature of some clients, authorization servers SHOULD NOT
make assumptions about the confidentiality of client credentials
without establishing trust with the client operator. Authorization
servers SHOULD NOT issue client secrets to clients incapable of
keeping their secrets confidential.
3.2. End-User Endpoint
In flows that involved an end-user, clients direct the end-user to
the end-user endpoint to approve their access request. When
accessing the end-user endpoint, the end-user first authenticates
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with the authorization server, and then approves or denies the access
request.
The way in which the authorization server authenticates the end-user
(e.g. username and password login, OpenID, session cookies) and in
which the authorization server obtains the end-user's authorization,
including whether it uses a secure channel such as TLS/SSL, is beyond
the scope of this specification. However, the authorization server
MUST first verify the identity of the end-user.
The URI of the end-user endpoint can be found in the service
documentation, or can be obtained by the client by making an
unauthorized protected resource request (from the "WWW-Authenticate"
response header "user-uri" attribute as described by Section 5.1).
The end-user endpoint advertised by the resource server MAY include a
query component as defined by [RFC3986] section 3, which must be
retained when adding additional query parameters.
Since requests to the end-user endpoint result in user authentication
and the transmission of sensitive values, the authorization server
SHOULD require the use of a transport-layer mechanism such as TLS/SSL
(or a secure channel with equivalent protections) when sending
requests to the end-user endpoint.
3.3. Token Endpoint
After obtaining authorization from the resource owner, clients
request an access token from the authorization server's token
endpoint.
The URI of the token endpoint can be found in the service
documentation, or can be obtained by the client by making an
unauthorized protected resource request (from the "WWW-Authenticate"
response header "token-uri" attribute as described by Section 5.1).
The token endpoint advertised by the resource server MAY include a
query component as defined by [RFC3986] section 3.
Since requests to the token endpoint result in the transmission of
plain text credentials in the HTTP request and response, the
authorization server MUST require the use of a transport-layer
mechanism such as TLS/SSL (or a secure channel with equivalent
protections) when sending requests to the token endpoints.
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3.3.1. Client Authentication
The token endpoint requires the client to authenticate itself to the
authorization server. This is done by including the client
identifier (and optional secret) in the request. The client
identifier and secret are included in the request using two request
parameters: "client_id" and "client_secret".
For example (line breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
type=web_server&client_id=s6BhdRkqt3&
client_secret=gX1fBat3bV&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
The client MAY include the client credentials using an HTTP
authentication scheme instead of using the "client_id" and
"client_secret" request parameters. Including the client credentials
using an HTTP authentication scheme fullfills the requirements of
including the parameters as defined by the various flows. The client
MUST NOT include the client credentials using more than one
mechanism.
The authorization server MUST accept the client credentials using
both the request parameters, and the HTTP Basic authentication scheme
as defined in [RFC2617]. The authorization server MAY support
additional HTTP authentication schemes.
For example (line breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
type=web_server&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
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3.3.2. Response Format
Authorization servers respond to client requests by including a set
of response parameters in the entity body of the HTTP response. The
response uses one of three formats based on the format requested by
the client (using the "format" request parameter):
o The "application/json" media type as defined by [RFC4627]. The
parameters are serialized into a JSON structure by adding each
parameter at the highest structure level. Parameter names and
string values are included as JSON strings. Numerical values are
included as JSON numbers.
For example:
{
"access_token":"SlAV32hkKG",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8"
}
o The "application/xml" media type as defined by [RFC3023]. The
parameters are serialized into an XML structure by adding each
parameter as a child element of the root "<OAuth>" element. [[ Add
namespace ]]
For example:
<?xml version='1.0' encoding="utf-8"?>
<OAuth>
<access_token>SlAV32hkKG</access_token>
<expires_in>3600</expires_in>
<refresh_token>8xLOxBtZp8</refresh_token>
</OAuth>
o The "application/x-www-form-urlencoded" media type as defined by
[W3C.REC-html40-19980424].
For example (line breaks are for display purposes only):
access_token=SlAV32hkKG&expires_in=3600&
refresh_token=8xLOxBtZp8
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The authorization server MUST include the HTTP "Cache-Control"
response header field with a value of "no-store" in any response
containing tokens, secrets, or other sensitive information.
3.3.2.1. Access Token Response
After receiving and verifying a valid and authorized access token
request from the client (as described in each of the flows below),
the authorization server constructs the response using the format
requested by the client, which includes the common parameters set as
well as additional flow-specific parameters. The formatted
parameters are sent to the client in the entity body of the HTTP
response with a 200 status code (OK).
The token response contains the following common parameters:
access_token
REQUIRED. The access token issued by the authorization server.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime.
refresh_token
OPTIONAL. The refresh token used to obtain new access tokens
using the same end-user access grant as described in Section 4.
access_token_secret
REQUIRED if requested by the client. The corresponding access
token secret as requested by the client.
scope
OPTIONAL. The scope of the access token as a list of space-
delimited strings. The value of the "scope" parameter is
defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
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For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8"
}
3.3.2.2. Error Response
If the token request is invalid or unauthorized, the authorization
server constructs a JSON-formatted response which includes the common
parameters set as well as additional flow-specific parameters. The
formatted parameters are sent to the client in the entity body of the
HTTP response with a 400 status code (Bad Request).
The response contains the following common parameter:
error
REQUIRED. The parameter value MUST be set to one of the values
specified by each flow.
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error":"incorrect_client_credentials"
}
3.4. Flow Parameters
The sizes of tokens and other values received from the authorization
server, are left undefined by this specification. Clients should
avoid making assumptions about value sizes. Servers should document
the expected size of any value they issue.
Unless otherwise noted, all the protocol parameter names and values
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are case sensitive.
3.5. User-Agent Flow
The user-agent flow is a user delegation flow suitable for client
applications residing in a user-agent, typically implemented in a
browser using a scripting language such as JavaScript. These clients
cannot keep client secrets confidential and the authentication of the
client is based on the user-agent's same-origin policy.
Unlike other flows in which the client makes separate authorization
and access token requests, the client received the access token as a
result of the authorization request in the form of an HTTP
redirection. The client requests the authorization server to
redirect the user-agent to another web server or local resource
accessible to the browser which is capable of extracting the access
token from the response and passing it to the client.
This user-agent flow does not utilize the client secret since the
client executables reside on the end-user's computer or device which
makes the client secret accessible and exploitable. Because the
access token is encoded into the redirection URI, it may be exposed
to the end-user and other applications residing on the computer or
device.
+----------+ Client Identifier +----------------+
| |>---(A)-- & Redirection URI --->| |
| | | |
End <--+ - - - +----(B)-- User authenticates -->| Authorization |
User | | | Server |
| |<---(C)-- Redirect URI --------<| |
| Client | with Access Token | |
| in | (w/ Optional Refresh Token) +----------------+
| Browser | in Fragment
| | +----------------+
| |>---(D)-- Redirect URI -------->| |
| | without Fragment | Web Server |
| | | with Client |
| (F) |<---(E)-- Web Page with -------<| Resource |
| Access | Script | |
| Token | +----------------+
+----------+
Figure 3
The user-agent flow illustrated in Figure 3 includes the following
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steps:
(A) The client sends the user-agent to the authorization server and
includes its client identifier and redirection URI in the
request.
(B) The authorization server authenticates the end-user (via the
user-agent) and establishes whether the end-user grants or
denies the client's access request.
(C) Assuming the end-user granted access, the authorization server
redirects the user-agent to the redirection URI provided
earlier. The redirection URI includes the access token in the
URI fragment.
(D) The user-agent follows the redirection instructions by making a
request to the web server which does not include the fragment.
The user-agent retains the fragment information locally.
(E) The web server returns a web page containing a script capable of
extracting the access token from the URI fragment retained by
the user-agent.
(F) The user-agent executes the script provided by the web server
which extracts the access token and passes it to the client.
3.5.1. Client Requests Authorization
In order for the end-user to grant the client access, the client
sends the end-user to the authorization server. The client
constructs the request URI by adding the following URI query
parameters to the end-user endpoint URI:
type
REQUIRED. The parameter value MUST be set to "user_agent".
client_id
REQUIRED. The client identifier as described in Section 3.1.
redirect_uri
REQUIRED unless a redirection URI has been established between
the client and authorization server via other means. An
absolute URI to which the authorization server will redirect
the user-agent to when the end-user authorization step is
completed. The authorization server SHOULD require the client
to pre-register their redirection URI. Authorization servers
MAY restrict the redirection URI to not include a query
component as defined by [RFC3986] section 3.
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state
OPTIONAL. An opaque value used by the client to maintain state
between the request and callback. The authorization server
includes this value when redirecting the user-agent back to the
client.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value of the "scope" parameter
is defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
immediate
OPTIONAL. The parameter value must be set to "true" or
"false". If set to "true", the authorization server MUST NOT
prompt the end-user to authenticate or approve access.
Instead, the authorization server attempts to establish the
end-user's identity via other means (e.g. browser cookies) and
checks if the end-user has previously approved an identical
access request by the same client and if that access grant is
still active. If the authorization server does not support an
immediate check or if it is unable to establish the end-user's
identity or approval status, it MUST deny the request without
prompting the end-user. Defaults to "false" if omitted.
secret_type
OPTIONAL. The access token secret type as described by
Section 5.3. If omitted, the authorization server will issue a
bearer token (an access token without a matching secret) as
described by Section 5.2.
The client directs the end-user to the constructed URI using an HTTP
redirection response, or by other means available to it via the end-
user's user-agent. The request MUST use the HTTP "GET" method.
For example, the client directs the end-user's user-agent to make the
following HTTPS request (line breaks are for display purposes only):
GET /authorize?type=user_agent&client_id=s6BhdRkqt3&
redirect_uri=https%3A%2F%2FEexample%2Ecom%2Frd HTTP/1.1
Host: server.example.com
If the client has previously registered a redirection URI with the
authorization server, the authorization server MUST verify that the
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redirection URI received matches the registered URI associated with
the client identifier.
The authorization server authenticates the end-user and obtains an
authorization decision (by asking the end-user or establishing
approval via other means). The authorization server sends the end-
user's user-agent to the provided client redirection URI using an
HTTP redirection response.
3.5.1.1. End-user Grants Authorization
If the end-user authorizes the access request, the authorization
server issues an access token and delivers it to the client by adding
the following parameters, using the
"application/x-www-form-urlencoded" format as defined by
[W3C.REC-html40-19980424], to the redirection URI fragment:
access_token
REQUIRED. The access token.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime.
refresh_token
OPTIONAL. The refresh token.
state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.
access_token_secret
REQUIRED if requested by the client. The corresponding access
token secret as requested by the client.
For example, the authorization server redirects the end-user's user-
agent by sending the following HTTP response:
HTTP/1.1 302 Found
Location: http://example.com/rd#access_token=FJQbwq9&expires_in=3600
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3.5.1.2. End-user Denies Authorization
If the end-user denied the access request, the authorization server
responds to the client by adding the following parameters, using the
"application/x-www-form-urlencoded" format as defined by
[W3C.REC-html40-19980424], to the redirection URI fragment:
error
REQUIRED. The parameter value MUST be set to "user_denied".
state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.
For example, the authorization server responds with the following:
HTTP/1.1 302 Found
Location: http://example.com/rd#error=user_denied
The authorization flow concludes unsuccessfully. To extract the
error message, the client follows the steps described in
Section 3.5.2.
3.5.2. Client Extracts Access Token
The user-agent follows the authorization server redirection response
by making an HTTP "GET" request to the URI received in the "Location"
HTTP response header. The user-agent SHALL NOT include the fragment
component with the request.
For example, the user-agent makes the following HTTP "GET" request in
response to the redirection directive received from the authorization
server:
GET /rd HTTP/1.1
Host: example.com
The HTTP response to the redirection request returns a web page
(typically an HTML page with an embedded script) capable of accessing
the full redirection URI including the fragment retained by the user-
agent, and extracting the access token (and other parameters)
contained in the fragment.
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3.6. Web Server Flow
The web server flow is a user delegation flow suitable for clients
capable of interacting with the end-user's user-agent (typically a
web browser) and capable of receiving incoming requests from the
authorization server (capable of acting as an HTTP server).
+----------+ Client Identifier +---------------+
| -+----(A)-- & Redirect URI ------->| |
| End-user | | Authorization |
| at |<---(B)-- User authenticates --->| Server |
| Browser | | |
| -+----(C)-- Verification Code ----<| |
+-|----|---+ +---------------+
| | ^ v
(A) (C) | |
| | | |
^ v | |
+---------+ | |
| |>---(D)-- Client Credentials, --------' |
| Web | Verification Code, |
| Client | & Redirect URI |
| | |
| |<---(E)------- Access Token -----------------'
+---------+ (w/ Optional Refresh Token)
Figure 4
The web server flow illustrated in Figure 4 includes the following
steps:
(A) The web client initiates the flow by redirecting the end-user's
user-agent to the end-user endpoint with its client identifier
and a redirect URI to which the authorization server will send
the end-user back once authorization is received (or denied).
(B) The authorization server authenticates the end-user (via the
user-agent) and establishes whether the end-user grants or
denies the client's access request.
(C) Assuming the end-user granted access, the authorization server
redirects the user-agent back to the client to the redirection
URI provided earlier. The authorization includes a verification
code for the client to use to obtain an access token.
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(D) The client requests an access token from the authorization
server by including its client credentials (identifier and
secret), as well as the verification code received in the
previous step.
(E) The authorization server validates the client credentials and
the verification code and responds back with the access token.
3.6.1. Client Requests Authorization
In order for the end-user to grant the client access, the client
sends the end-user to the authorization server. The client
constructs the request URI by adding the following URI query
parameters to the end-user endpoint URI:
type
REQUIRED. The parameter value MUST be set to "web_server".
client_id
REQUIRED. The client identifier as described in Section 3.1.
redirect_uri
REQUIRED unless a redirection URI has been established between
the client and authorization server via other means. An
absolute URI to which the authorization server will redirect
the user-agent to when the end-user authorization step is
completed. The authorization server MAY require the client to
pre-register their redirection URI. Authorization servers MAY
restrict the redirection URI to not include a query component
as defined by [RFC3986] section 3.
state
OPTIONAL. An opaque value used by the client to maintain state
between the request and callback. The authorization server
includes this value when redirecting the user-agent back to the
client.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value of the "scope" parameter
is defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
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immediate
OPTIONAL. The parameter value must be set to "true" or
"false". If set to "true", the authorization server MUST NOT
prompt the end-user to authenticate or approve access.
Instead, the authorization server attempts to establish the
end-user's identity via other means (e.g. browser cookies) and
checks if the end-user has previously approved an identical
access request by the same client and if that access grant is
still active. If the authorization server does not support an
immediate check or if it is unable to establish the end-user's
identity or approval status, it MUST deny the request without
prompting the end-user. Defaults to "false" if omitted.
The client directs the end-user to the constructed URI using an HTTP
redirection response, or by other means available to it via the end-
user's user-agent. The request MUST use the HTTP "GET" method.
For example, the client directs the end-user's user-agent to make the
following HTTPS requests (line breaks are for display purposes only):
GET /authorize?type=web_server&client_id=s6BhdRkqt3&redirect_uri=
https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com
If the client has previously registered a redirection URI with the
authorization server, the authorization server MUST verify that the
redirection URI received matches the registered URI associated with
the client identifier.
The authorization server authenticates the end-user and obtains an
authorization decision (by asking the end-user or establishing
approval via other means). The authorization server sends the end-
user's user-agent to the provided client redirection URI using an
HTTP redirection response, or by other means available to it via the
end-user's user-agent.
3.6.1.1. End-user Grants Authorization
If the end-user authorizes the access request, the authorization
server generates a verification code and associates it with the
client identifier and redirection URI. The authorization server
constructs the request URI by adding the following parameters to the
query component of redirection URI provided by the client:
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code
REQUIRED. The verification code generated by the authorization
server.
state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.
The verification code should expire shortly after it is issued and
allowed for a single use.
For example, the authorization server redirects the end-user's user-
agent by sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb?code=i1WsRn1uB1
In turn, the end-user's user-agent makes the following HTTPS "GET"
request:
GET /cb?code=i1WsRn1uB1 HTTP/1.1
Host: client.example.com
3.6.1.2. End-user Denies Authorization
If the end-user denied the access request, the authorization server
constructs the request URI by adding the following parameters to the
query component of the redirection URI provided by the client:
error
REQUIRED. The parameter value MUST be set to "user_denied".
state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.
For example, the authorization server directs the client to make the
following HTTP request:
GET /cb?error=user_denied HTTP/1.1
Host: client.example.com
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The authorization flow concludes unsuccessfully.
3.6.2. Client Requests Access Token
The client obtains an access token from the authorization server by
making an HTTP "POST" request to the token endpoint. The client
constructs a request URI by adding the following parameters to the
request:
type
REQUIRED. The parameter value MUST be set to "web_server".
client_id
REQUIRED. The client identifier as described in Section 3.1.
client_secret
REQUIRED if the client identifier has a matching secret. The
client secret as described in Section 3.1.
code
REQUIRED. The verification code received from the
authorization server.
redirect_uri
REQUIRED. The redirection URI used in the initial request.
secret_type
OPTIONAL. The access token secret type as described by
Section 5.3. If omitted, the authorization server will issue a
bearer token (an access token without a matching secret) as
described by Section 5.2.
format
OPTIONAL. The response format requested by the client. Value
MUST be one of "json", "xml", or "form". Defaults to "json" if
no omitted.
For example, the client makes the following HTTPS request (line
breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
type=web_server&client_id=s6BhdRkqt3&
client_secret=gX1fBat3bV&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
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The authorization server MUST verify that the verification code,
client identity, client secret, and redirection URI are all valid and
match its stored association. If the request is valid, the
authorization server issues a successful response as described in
Section 3.3.2.1.
For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8"
}
If the request is invalid, the authorization server returns an error
response as described in Section 3.3.2.2 with one of the following
error codes:
o "redirect_uri_mismatch"
o "bad_verification_code"
o "incorrect_client_credentials"
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error":"incorrect_client_credentials"
}
3.7. Device Flow
The device flow is a user delegation flow suitable for clients
executing on devices which do not have an easy data-entry method
(e.g. game consoles or media hub), but where the end-user has
separate access to a user-agent on another computer or device (e.g.
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home computer, a laptop, or a smart phone). The client is incapable
of receiving incoming requests from the authorization server
(incapable of acting as an HTTP server).
Instead of interacting with the end-user's user-agent, the client
instructs the end-user to use another computer or device and connect
to the authorization server to approve the access request. Since the
client cannot receive incoming requests, it polls the authorization
server repeatedly until the end-user completes the approval process.
This device flow does not utilize the client secret since the client
executables reside on a local device which makes the client secret
accessible and exploitable.
+----------+ +----------------+
| |>---(A)-- Client Identifier --->| |
| | | |
| |<---(B)-- Verification Code, --<| |
| | User Code, | |
| | & Verification URI | |
| Device | | |
| Client | Client Identifier & | |
| |>---(E)-- Verification Code --->| |
| | ... | |
| |>---(E)---> | |
| | | Authorization |
| |<---(F)-- Access Token --------<| Server |
+----------+ (w/ Optional Refresh Token) | |
v | |
: | |
(C) User Code & Verification URI | |
: | |
v | |
+----------+ | |
| End-user | | |
| at |<---(D)-- User authenticates -->| |
| Browser | | |
+----------+ +----------------+
Figure 5
The device flow illustrated in Figure 5 includes the following steps:
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(A) The client requests access from the authorization server and
includes its client identifier in the request.
(B) The authorization server issues a verification code, an end-user
code, and provides the end-user verification URI.
(C) The client instructs the end-user to use its user-agent
(elsewhere) and visit the provided end-user verification URI.
The client provides the end-user with the end-user code to enter
in order to grant access.
(D) The authorization server authenticates the end-user (via the
user-agent) and prompts the end-user to grant the client's
access request. If the end-user agrees to the client's access
request, the end-user enters the end-user code provided by the
client. The authorization server validates the end-user code
provided by the end-user.
(E) While the end-user authorizes (or denies) the client's request
(D), the client repeatedly polls the authorization server to
find out if the end-user completed the end-user authorization
step. The client includes the verification code and its client
identifier.
(F) Assuming the end-user granted access, the authorization server
validates the verification code provided by the client and
responds back with the access token.
3.7.1. Client Requests Authorization
The client initiates the flow by requesting a set of verification
codes from the authorization server by making an HTTP "POST" request
to the token endpoint. The client constructs a request URI by adding
the following parameters to the request:
type
REQUIRED. The parameter value MUST be set to "device_code".
client_id
REQUIRED. The client identifier as described in Section 3.1.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value of the "scope" parameter
is defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
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format
OPTIONAL. The response format requested by the client. Value
MUST be one of "json", "xml", or "form". Defaults to "json" if
no omitted.
For example, the client makes the following HTTPS request (line
breaks are for display purposes only):
POST /token?type=device_code&client_id=s6BhdRkqt3
HTTP/1.1
Host: server.example.com
In response, the authorization server generates a verification code
and an end-user code and includes them in the HTTP response body
using the "application/json" format as described by Section 3.3.2
with a 200 status code (OK). The response contains the following
parameters:
code
REQUIRED. The verification code.
user_code
REQUIRED. The end-user code.
verification_uri
REQUIRED. The end-user verification URI on the authorization
server. The URI should be short and easy to remember as end-
users will be asked to manually type it into their user-agent.
expires_in
OPTIONAL. The duration in seconds of the verification code
lifetime.
interval
OPTIONAL. The minimum amount of time in seconds that the
client SHOULD wait between polling requests to the token
endpoint.
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For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"code":"74tq5miHKB",
"user_code":"94248",
"verification_uri":"http://www.example.com/device",
"interval"=5
}
The client displays the end-user code and the end-user verification
URI to the end-user, and instructs the end-user to visit the URI
using a user-agent and enter the end-user code.
The end-user manually types the provided verification URI and
authenticates with the authorization server. The authorization
server prompts the end-user to authorize the client's request by
entering the end-user code provided by the client. Once the end-user
approves or denies the request, the authorization server informs the
end-user to return to the device for further instructions.
3.7.2. Client Requests Access Token
Since the client is unable to receive incoming requests from the
authorization server, it polls the authorization server repeatedly
until the end-user grants or denies the request, or the verification
code expires.
The client makes the following request at an arbitrary but reasonable
interval which MUST NOT exceed the minimum interval rate provided by
the authorization server (if present via the "interval" parameter).
Alternatively, the client MAY provide a user interface for the end-
user to manually inform it when authorization was granted.
The client requests an access token by making an HTTP "POST" request
to the token endpoint. The client constructs a request URI by adding
the following parameters to the request:
type
REQUIRED. The parameter value MUST be set to "device_token".
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client_id
REQUIRED. The client identifier as described in Section 3.1.
code
The verification code received from the authorization server.
secret_type
OPTIONAL. The access token secret type as described by
Section 5.3. If omitted, the authorization server will issue a
bearer token (an access token without a matching secret) as
described by Section 5.2.
format
OPTIONAL. The response format requested by the client. Value
MUST be one of "json", "xml", or "form". Defaults to "json" if
no omitted.
For example, the client makes the following HTTPS request (line
breaks are for display purposes only):
POST /token?type=device_token&client_id=s6BhdRkqt3
&code=74tq5miHKB HTTP/1.1
Host: server.example.com
If the end-user authorized the request, the authorization server
issues an access token response as described in Section 3.3.2.1.
For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8"
}
If the request is invalid, the authorization server returns an error
response as described in Section 3.3.2.2 with one of the following
error codes:
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o "authorization_declined"
o "bad_verification_code"
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error":"authorization_declined"
}
If the end-user authorization is pending or expired without receiving
any response from the end-user, or the client is exceeding the
allowed polling interval, the authorization server returns an error
response as described in Section 3.3.2.2 with one of the following
error codes:
o "'authorization_pending"
o "slow_down"
o "code_expired"
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error":"authorization_pending"
}
3.8. Username and Password Flow
The username and password flow is suitable for clients capable of
asking end-users for their usernames and passwords. It is also used
to migrate existing clients using direct authentication schemes such
as HTTP Basic or Digest authentication to OAuth by converting the
end-user credentials stored with tokens.
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However, unlike the HTTP Basic authentication scheme defined in
[RFC2617], the end-user's credentials are used in a single request
and are exchanged for an access token and refresh token which
eliminates the client need to store them for future use.
The methods through which the client prompts end users for their
usernames and passwords is beyond the scope of this specification.
The client MUST discard the usernames and passwords once an access
token has been obtained.
This flow is suitable in cases where the end-user already has a trust
relationship with the client, such as its computer operating system
or highly privileged applications. Authorization servers should take
special care when enabling the username and password flow, and only
when other delegation flows are not viable.
End-user
v
:
(A)
:
v
+--------+ +---------------+
| | Client Credentials | |
| |>--(B)--- & User Credentials ---->| Authorization |
| Client | | Server |
| |<--(C)---- Access Token ---------<| |
| | (w/ Optional Refresh Token) | |
+--------+ +---------------+
Figure 6
The username and password flow illustrated in Figure 6 includes the
following steps:
(A) The end-user provides the client with its username and password.
(B) The client sends an access token request to the authorization
server and includes its client identifier and client secret, and
the end-user's username and password.
(C) The authorization server validates the end-user credentials and
the client credentials and issues an access token.
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3.8.1. Client Requests Access Token
The client requests an access token by making an HTTP "POST" request
to the token endpoint. The client constructs a request URI by adding
the following parameters to the request:
type
REQUIRED. The parameter value MUST be set to "username".
client_id
REQUIRED. The client identifier as described in Section 3.1.
client_secret
REQUIRED. The client secret as described in Section 3.1.
OPTIONAL if no client secret was issued.
username
REQUIRED. The end-user's username.
password
REQUIRED. The end-user's password.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value of the "scope" parameter
is defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
secret_type
OPTIONAL. The access token secret type as described by
Section 5.3. If omitted, the authorization server will issue a
bearer token (an access token without a matching secret) as
described by Section 5.2.
format
OPTIONAL. The response format requested by the client. Value
MUST be one of "json", "xml", or "form". Defaults to "json" if
no omitted.
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For example, the client makes the following HTTPS request (line
breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
type=username&client_id=s6BhdRkqt3&client_secret=
47HDu8s&username=johndoe&password=A3ddj3w
The authorization server MUST validate the client credentials and
end-user credentials and if valid issues an access token response as
described in Section 3.3.2.1.
For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8"
}
If the request is invalid, the authorization server returns an error
response as described in Section 3.3.2.2 with one of the following
error codes:
o "incorrect_client_credentials"
o "unauthorized_client'" - The client is not permitted to use this
flow.
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error":"incorrect_client_credentials"
}
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3.9. Client Credentials Flow
The client credentials flow is used when the client acts on behalf of
itself (the client is the resource owner), or when the client
credentials are used to obtain an access token representing a
previously established access authorization. The client secret is
assumed to be high-entropy since it is not designed to be memorized
by an end-user.
+--------+ +---------------+
| | | |
| |>--(A)--- Client Credentials ---->| Authorization |
| Client | | Server |
| |<--(B)---- Access Token ---------<| |
| | (w/ Optional Refresh Token) | |
+--------+ +---------------+
Figure 7
The client credential flow illustrated in Figure 7 includes the
following steps:
(A) The client sends an access token request to the authorization
server and includes its client identifier and client secret.
(B) The authorization server validates the client credentials and
issues an access token.
3.9.1. Client Requests Access Token
The client requests an access token by making an HTTP "POST" request
to the token endpoint. The client constructs a request URI by adding
the following parameters to the request:
type
REQUIRED. The parameter value MUST be set to
"client_credentials".
client_id
REQUIRED. The client identifier as described in Section 3.1.
client_secret
REQUIRED. The client secret as described in Section 3.1.
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scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value of the "scope" parameter
is defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
secret_type
OPTIONAL. The access token secret type as described by
Section 5.3. If omitted, the authorization server will issue a
bearer token (an access token without a matching secret) as
described by Section 5.2.
format
OPTIONAL. The response format requested by the client. Value
MUST be one of "json", "xml", or "form". Defaults to "json" if
no omitted.
For example, the client makes the following HTTPS request:
POST /token HTTP/1.1
Host: server.example.com
type=client_credentials&client_id=s6BhdRkqt3&client_secret=47HDu8s
The authorization server MUST validate the client credentials and if
valid issues an access token response as described in
Section 3.3.2.1.
For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8"
}
If the request is invalid, the authorization server returns an error
response as described in Section 3.3.2.2 with one of the following
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error codes:
o "incorrect_client_credentials"
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error":"incorrect_client_credentials"
}
3.10. Assertion Flow
The assertion flow is used when a client wishes to exchange an
existing security token or assertion for an access token. This flow
is suitable when the client is the resource owner or is acting on
behalf of the resource owner (based on the content of the assertion
used).
The assertion flow requires the client to obtain a assertion (such as
a SAML [OASIS.saml-core-2.0-os] assertion) from an assertion issuer
or to self-issue an assertion prior to initiating the flow. The
assertion format, the process by which the assertion is obtained, and
the method of validating the assertion are defined by the assertion
issuer and the authorization server, and are beyond the scope of this
specification.
+--------+ +---------------+
| | | |
| |>--(A)------ Assertion ---------->| Authorization |
| Client | | Server |
| |<--(B)---- Access Token ---------<| |
| | | |
+--------+ +---------------+
Figure 8
The assertion flow illustrated in Figure 8 includes the following
steps:
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(A) The client sends an access token request to the authorization
server and includes an assertion.
(B) The authorization server validates the assertion and issues an
access token.
3.10.1. Client Requests Access Token
The client requests an access token by making an HTTP "POST" request
to the token endpoint. The client constructs a request URI by adding
the following parameters to the request:
type
REQUIRED. The parameter value MUST be set to "assertion".
format
REQUIRED. The format of the assertion as defined by the
authorization server. The value MUST be an absolute URI.
assertion
REQUIRED. The assertion.
client_id
OPTIONAL. The client identifier as described in Section 3.1.
The authorization server MAY require including the client
credentials with the request based on the assertion properties.
client_secret
OPTIONAL. The client secret as described in Section 3.1. MUST
NOT be included if the "client_id" parameter is omitted.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value of the "scope" parameter
is defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
secret_type
OPTIONAL. The access token secret type as described by
Section 5.3. If omitted, the authorization server will issue a
bearer token (an access token without a matching secret) as
described by Section 5.2.
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format
OPTIONAL. The response format requested by the client. Value
MUST be one of "json", "xml", or "form". Defaults to "json" if
no omitted.
For example, the client makes the following HTTPS request (line
breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
type=assertion&format=_______&assertion=_______
The authorization server MUST validate the assertion and if valid
issues an access token response as described in Section 3.3.2.1. The
authorization server SHOULD NOT issue a refresh token.
For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"expires_in":3600
}
If the request is invalid, the authorization server returns an error
response as described in Section 3.3.2.2 with one of the following
error codes:
o "invalid_assertion"
o "unknown_format"
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For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error":"invalid_assertion"
}
Authorization servers SHOULD issue access tokens with a limited
lifetime and require clients to refresh them by requesting a new
access token using the same assertion if it is still valid.
Otherwise the client MUST obtain a new valid assertion.
4. Refreshing an Access Token
Token refresh is used when the lifetime of an access token is shorter
than the lifetime of the authorization grant. It allows clients to
obtain a new access token without having to go through the
authorization flow again or involve the resource owner. It is also
used to obtain a new token with different security properties (e.g.
bearer token, token with shared symmetric secret).
+--------+ Client Credentials, +---------------+
| | Refresh Token, | |
| |>--(A)----- & Secret Type ------->| Authorization |
| Client | | Server |
| |<--(B)----- Access Token --------<| |
| | & Optional Secret | |
+--------+ +---------------+
Figure 9
To refresh a token, the client constructs an HTTP "POST" request to
the token endpoint and includes the following parameters in the HTTP
request body using the "application/x-www-form-urlencoded" content
type as defined by [W3C.REC-html40-19980424]:
type
REQUIRED. The parameter value MUST be set to "refresh".
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client_id
REQUIRED. The client identifier as described in Section 3.1.
client_secret
REQUIRED if the client was issued a secret. The client secret.
refresh_token
REQUIRED. The refresh token associated with the access token
to be refreshed.
secret_type
OPTIONAL. The access token secret type as described by
Section 5.3. If omitted, the authorization server will issue a
bearer token (an access token without a matching secret) as
described by Section 5.2.
format
OPTIONAL. The response format requested by the client. Value
MUST be one of "json", "xml", or "form". Defaults to "json" if
no omitted.
For example, the client makes the following HTTPS request (line break
are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
type=refresh_token&client_id=s6BhdRkqt3&client_secret=8eSEIpnqmM
&refresh_token=n4E9O119d&secret_type=hmac-sha256
verify the client credential, the validity of the refresh token, and
that the resource owner's authorization is still valid. If the
request is valid, the authorization server issues an access token
response as described in Section 3.3.2.1. The authorization server
MAY issue a new refresh token in which case the client MUST NOT use
the previous refresh token and replace it with the newly issued
refresh token.
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For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"expires_in":3600
}
If the request is invalid, the authorization server returns an error
response as described in Section 3.3.2.2 with one of the following
error codes:
o "incorrect_client_credentials"
o "authorization_expired"
o "unsupported_secret_type"
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error":"incorrect_client_credentials"
}
5. Accessing a Protected Resource
Clients access protected resources by presenting an access token to
the resource server. The methods used by the resource server to
validate the access token are beyond the scope of this specification,
but generally involve an interaction or coordination between the
resource server and authorization server.
The method in which a client uses an access token depends on the
security properties of the access tokens. By default, access tokens
are issued without a matching secret. Clients MAY request an access
token with a matching secret by specifying the desired secret type
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using the "secret_type" token request parameter.
When an access token does not include a matching secret, the access
token acts as a bearer token, where the token string is a shared
symmetric secret. This requires treating the access token with the
same care as other secrets (e.g. user passwords). Access tokens
SHOULD NOT be sent in the clear over an insecure channel.
However, when it is necessary to transmit bearer tokens in the clear
without a secure channel, authorization servers SHOULD issue access
tokens with limited scope and lifetime to reduce the potential risk
from a compromised access token. Clients SHOULD request and utilize
an access token with a matching secret when making protected resource
requests over an insecure channel (e.g. an HTTP request without using
TLS/SSL).
When an access token includes a matching secret, the secret is not
included directly in the request but is used instead to generate a
cryptographic signature of the request. The signature can only be
generated and verified by entities with access to the secret.
Clients SHOULD NOT make authenticated requests with an access token
to unfamiliar resource servers, especially when using bearer tokens,
regardless of the presence of a secure channel.
5.1. The Authorization Request Header
The "Authorization" request header field is used by clients to make
both bearer token and cryptographic token requests. When making
bearer token requests, the client uses the "token" attribute to
include the access token in the request without any of the other
attributes. Additional methods for making bearer token requests are
described in Section 5.2.
For example:
GET /resource HTTP/1.1
Host: server.example.com
Authorization: Token token="vF9dft4qmT"
When making a cryptographic token request (using an access token with
a matching secret) the client uses the "token" attribute to include
the access token in the request, and uses the "nonce", "timestamp",
"algorithm", and "signature" attributes to apply the matching secret.
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For example:
GET /resource HTTP/1.1
Host: server.example.com
Authorization: Token token="vF9dft4qmT",
nonce="s8djwd",
timestamp="137131200",
algorithm="hmac-sha256",
signature="wOJIO9A2W5mFwDgiDvZbTSMK/PY="
The "Authorization" header field uses the framework defined by
[RFC2617] as follows:
credentials = "Token" RWS token-response
token-response = token-id
[ CS nonce ]
[ CS timestamp ]
[ CS algorithm ]
[ CS signature ]
token-id = "token" "=" <"> token <">
timestamp = "timestamp" "=" <"> 1*DIGIT <">
nonce = "nonce" "=" <"> token <">
algorithm = "algorithm" "=" algorithm-name
algorithm-name = "hmac-sha256" /
token
signature = "signature" "=" <"> token <">
5.2. Bearer Token Requests
Clients make bearer token requests by including the access token
using the HTTP "Authorization" request header with the "Token"
authentication scheme as described in Section 5.1. The access token
is included using the "token" parameter.
For example, the client makes the following HTTPS request:
GET /resource HTTP/1.1
Host: server.example.com
Authorization: Token token="vF9dft4qmT"
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The resource server MUST validate the access token and ensure it has
not expired and that its scope covers the requested resource. If the
token expired or is invalid, the resource server MUST reply with an
HTTP 401 status code (Unauthorized) and include the HTTP
"WWW-Authenticate" response header as described in Section 6.1.
For example:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Token realm='Service', error='token_expired'
Alternatively, the client MAY include the access token using the HTTP
request URI in the query component as described in Section 5.2.1, or
in the HTTP body when using the "application/x-www-form-urlencoded"
content type as described in Section 5.2.2. Clients SHOULD only use
the request URI or body when the "Authorization" request header is
not available, and MUST NOT use more than one method in each request.
5.2.1. 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 HTTPS request:
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
appended following the request-specific parameters, properly
separated by an "&" character (ASCII code 38).
The resource server MUST validate the access token and ensure it has
not expired and its scope includes the requested resource. If the
resource expired or is not valid, the resource server MUST reply with
an HTTP 401 status code (Unauthorized) and include the HTTP
"WWW-Authenticate" response header as described in Section 6.1.
5.2.2. 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
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"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-html40-19980424].
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 HTTPS request:
POST /resource HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
oauth_token=vF9dft4qmT
The resource server MUST validate the access token and ensure it has
not expired and its scope includes the requested resource. If the
resource expired or is not valid, the resource server MUST reply with
an HTTP 401 status code (Unauthorized) and include the HTTP
"WWW-Authenticate" response header as described in Section 6.1.
5.3. Cryptographic Tokens Requests
Clients make authenticated protected resource requests using an
access token with a matching secret by calculating a set of values
and including them in the request using the "Authorization" header
field. The way clients calculate these values depends on the access
token secret type as issued by the authorization server.
This specification defines the "hmac-sha256" algorithm, and
establishes a registry for providing additional algorithms. Clients
obtain an access token with a matching "hmac-sha256" secret by using
the "secret_type" parameter when requesting an access token.
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5.3.1. The 'hmac-sha256' Algorithm
The "hmac-sha256" algorithm uses the HMAC method as defined in
[RFC2104] together with the SHA-256 hash function defined in [NIST
FIPS-180-3] to apply the access token secret to the request and
generate a signature value that is included in the request instead of
transmitting the secret in the clear.
To use the "hmac-sha256" algorithm, clients:
1. Calculate the request timestamp and generate a request nonce as
described in Section 5.3.1.1.
2. Construct the normalized request string as described in
Section 5.3.1.2.
3. Calculate the request signature as described in Section 5.3.1.3.
4. Include the timestamp, nonce, algorithm name, and calculated
signature in the request using the "Authorization" header field.
For example:
GET /resource HTTP/1.1
Host: server.example.com
Authorization: Token token="vF9dft4qmT",
nonce="s8djwd",
timestamp="137131200",
algorithm="hmac-sha256",
signature="wOJIO9A2W5mFwDgiDvZbTSMK/PY="
The resource server MUST validate the access token and ensure it has
not expired and that its scope covers the requested resource. The
resource server MUST also recalculate the request signature using the
attributes provided by the client and compare it to the signature
provided. If the token expired or is invalid, or if the signature is
incorrect, the resource server MUST reply with an HTTP 401 status
code (Unauthorized) and include the HTTP "WWW-Authenticate" response
header as described in Section 6.1.
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For example:
HTTP/1.1 401 Unauthorized
Date: Tue, 15 Nov 2010 08:12:31 GMT
WWW-Authenticate: Token realm='Service',
algorithms='hmac-sha256',
error='invalid_signature'
[[ Errors list ]]
5.3.1.1. Nonce and Timestamp
A timestamp in combination with unique nonce values is used to
protect against replay attacks when transmitted over an insecure
channel.
The nonce is a random string, uniquely generated by the client to
allow the resource server to verify that a request has never been
made before and helps prevent replay attacks when requests are made
over a non-secure channel. The nonce value MUST be unique across all
requests with the same timestamp and token combinations.
The timestamp value is the current time expressed in the number of
seconds since January 1, 1970 00:00:00 GMT, and MUST be a positive
integer.
To avoid the need to retain an infinite number of nonce values for
future checks, resource servers MAY choose to restrict the time
period after which a request with an old timestamp is rejected. When
resource servers apply such a restriction, clients SHOULD synchronize
their clocks by using the resource server's time as indicated by the
HTTP "Date" response header field as defined in [RFC2616].
5.3.1.2. Normalized String Construction
The normalized request string is a consistent, reproducible
concatenation of several of the HTTP request elements into a single
string. The string is used as an input to the selected cryptographic
method and includes the HTTP request method (e.g. "GET", "POST",
etc.), the authority as declared by the HTTP "Host" request header,
and the request resource URI.
The normalized request string does not cover the entire HTTP request.
Most notably, it does not include the entity-body or most HTTP
entity-headers. It is important to note that the resource server
cannot verify the authenticity of the excluded request elements
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without using additional protections such as TLS/SSL.
The normalized request string is constructed by concatenating
together, in order, the following HTTP request elements, separated by
the "," character (ASCII code 44):
1. The request timestamp as described in Section 5.3.1.1.
2. The request nonce as described in Section 5.3.1.1.
3. The cryptographic algorithm used.
4. The HTTP request method in uppercase. For example: "HEAD",
"GET", "POST", etc.
5. The hostname, colon-separated (ASCII code 58) from the TCP port
used to make the request as included in the HTTP request "Host"
header field. The port MUST be included even if it is not
included in the "Host" header field (i.e. the default port for
the scheme).
6. The request resource URI.
For example, the normalized request string for the "GET" request URI
"http://example.com/resource", request timestamp "137131200", request
nonce "s8djwd", and "hmac-sha256" algorithm (line breaks are for
display purposes only):
137131200,s8djwd,hmac-sha256,GET,example.com:80,
http://example.com/resource
5.3.1.3. Signature Calculation
Clients calculate the request signature using the HMAC-SHA256
function:
digest = HMAC-SHA256 (key, text)
by setting the function variables are follows:
text
is set to the value of the normalize request string as
described in Section 5.3.1.2.
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key
is set to the access token secret.
The request signature is the calculated value of the "digest"
variable after the result octet string is base64-encoded per
[RFC2045] section 6.8.
6. Identifying a Protected Resource
Clients access protected resources after locating the appropriate
end-user and token endpoints and obtaining an access token. In many
cases, interacting with a protected resource requires prior knowledge
of the protected resource properties and methods, as well as its
authentication requirements (i.e. establishing client identity,
locating the end-user and token endpoints).
However, there are cases in which clients are unfamiliar with the
protected resource, including whether the resource requires
authentication. When clients attempt to access an unfamiliar
protected resource without an access token, the resource server
denies the request and informs the client of the required credentials
using an HTTP authentication challenge.
In addition, when receiving an invalid authenticated request, the
resource server issues an authentication challenge including the
error type and message.
6.1. The WWW-Authenticate Response Header
A resource server receiving a request for a protected resource
without a valid access token MUST respond with a 401 (Unauthorized)
or 403 (Forbidden) HTTP status code, and include at least one "Token"
"WWW-Authenticate" response header field challenge.
The "WWW-Authenticate" header field uses the framework defined by
[RFC2617] as follows:
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challenge = "Token" RWS token-challenge
token-challenge = realm
[ CS user-uri ]
[ CS token-uri ]
[ CS algorithms ]
[ CS scope ]
[ CS error ]
user-uri = "user-uri" "=" URI-Reference
token-uri = "token-uri" "=" URI-Reference
algorithms = "algorithms" "=" <"> 1#algorithm-name <">
scope = "scope" "=" <"> 1#URI-Reference <">
error = "error" "=" <"> token <">
CS = OWS "," OWS
The "realm" attribute is used to provide the protected resources
partition as defined by [RFC2617].
The "user-uri" and "token-uri" attributes provide a way for the
resource server to advertise the URIs of the end-user and token
endpoints capable of issuing an access token suitable for accessing
the requested resource.
The "algorithms" attribute is a space-delimited list of the
cryptographic algorithms supported by the resource server. The
client MAY request an access token with a suitable matching secret by
using the "secret_type" request parameter as described in
Section 5.3.
The "scope" attribute is a space-delimited list of URIs (relative or
absolute) indicating the required scope of the access token for
accessing the requested resource.
The "error" attribute is used to inform the client the reason why an
access request was declined. [[ Add list of error codes ]]
7. Security Considerations
[[ Todo ]]
8. IANA Considerations
[[ Not Yet ]]
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9. Acknowledgements
[[ Add OAuth 1.0a authors + WG contributors ]]
Appendix A. Differences from OAuth 1.0a
[[ Todo ]]
Appendix B. Document History
[[ to be removed by RFC editor before publication as an RFC ]]
-05
o Corrected device example.
o Added client credentials parameters to the assertion flow as
OPTIONAL.
o Added the ability to send client credentials using an HTTP
authentication scheme.
o Initial text for the "WWW-Authenticate" header (also added scope
support).
o Change authorization endpoint to end-user endpoint.
o In the device flow, change the "user_uri" parameter to
"verification_uri" to avoid confusion with the end-user endpoint.
o Add "format" request parameter and support for XML and form-
encoded responses.
-04
o Changed all token endpoints to use "POST"
o Clarified the authorization server's ability to issue a new
refresh token when refreshing a token.
o Changed the flow categories to clarify the autonomous group.
o Changed client credentials language not to always be server-
issued.
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o Added a "scope" response parameter.
o Fixed typos.
o Fixed broken document structure.
-03
o Fixed typo in JSON error examples.
o Fixed general typos.
o Moved all flows sections up one level.
-02
o Removed restriction on "redirect_uri" including a query.
o Added "scope" parameter.
o Initial proposal for a JSON-based token response format.
-01
o Editorial changes based on feedback from Brian Eaton, Bill Keenan,
and Chuck Mortimore.
o Changed device flow "type" parameter values and switch to use only
the token endpoint.
-00
o Initial draft based on a combination of WRAP and OAuth 1.0a.
10. References
10.1. 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.
[NIST FIPS-180-3]
National Institute of Standards and Technology, "Secure
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Hash Standard (SHS). FIPS PUB 180-3, October 2008".
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[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.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[W3C.REC-html40-19980424]
Hors, A., Raggett, D., and I. Jacobs, "HTML 4.0
Specification", World Wide Web Consortium
Recommendation REC-html40-19980424, April 1998,
<http://www.w3.org/TR/1998/REC-html40-19980424>.
Hammer-Lahav, et al. Expires November 14, 2010 [Page 54]
Internet-Draft OAuth 2.0 May 2010
10.2. Informative References
[I-D.hammer-oauth]
Hammer-Lahav, E., "The OAuth 1.0 Protocol",
draft-hammer-oauth-10 (work in progress), February 2010.
[I-D.hardt-oauth]
Hardt, D., Tom, A., Eaton, B., and Y. Goland, "OAuth Web
Resource Authorization Profiles", draft-hardt-oauth-01
(work in progress), January 2010.
[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.
Authors' Addresses
Eran Hammer-Lahav (editor)
Yahoo!
Email: eran@hueniverse.com
URI: http://hueniverse.com
David Recordon
Facebook
Email: davidrecordon@facebook.com
URI: http://www.davidrecordon.com/
Dick Hardt
Email: dick.hardt@gmail.com
URI: http://dickhardt.org/
Hammer-Lahav, et al. Expires November 14, 2010 [Page 55]
