Network Working Group E. Hammer-Lahav, Ed.
Internet-Draft Yahoo!
Intended status: Standards Track D. Recordon
Expires: October 31, 2010 Facebook
D. Hardt
April 29, 2010
The OAuth 2.0 Protocol
draft-ietf-oauth-v2-00
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 October 31, 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.
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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 . . . . . . . . . . . . . . . . . . 8
3.1. Authorization Endpoint . . . . . . . . . . . . . . . . . . 9
3.2. Token Endpoint . . . . . . . . . . . . . . . . . . . . . . 9
3.3. Flow Parameters . . . . . . . . . . . . . . . . . . . . . 10
3.4. Client Credentials . . . . . . . . . . . . . . . . . . . . 10
3.5. User Delegation Flows . . . . . . . . . . . . . . . . . . 11
3.5.1. User-Agent Flow . . . . . . . . . . . . . . . . . . . 11
3.5.2. Web Server Flow . . . . . . . . . . . . . . . . . . . 15
3.5.3. Device Flow . . . . . . . . . . . . . . . . . . . . . 21
3.6. End User Credentials Flows . . . . . . . . . . . . . . . . 27
3.6.1. Username and Password Flow . . . . . . . . . . . . . . 27
3.7. Autonomous Client Flows . . . . . . . . . . . . . . . . . 30
3.7.1. Client Credentials Flow . . . . . . . . . . . . . . . 30
3.7.2. Assertion Flow . . . . . . . . . . . . . . . . . . . . 33
4. Refreshing an Access Token . . . . . . . . . . . . . . . . . . 35
5. Accessing a Protected Resource . . . . . . . . . . . . . . . . 38
5.1. The Authorization Request Header . . . . . . . . . . . . . 38
5.2. Bearer Token Requests . . . . . . . . . . . . . . . . . . 40
5.2.1. URI Query Parameter . . . . . . . . . . . . . . . . . 40
5.2.2. Form-Encoded Body Parameter . . . . . . . . . . . . . 41
5.3. Cryptographic Tokens Requests . . . . . . . . . . . . . . 42
5.3.1. The 'hmac-sha256' Algorithm . . . . . . . . . . . . . 42
6. Identifying a Protected Resource . . . . . . . . . . . . . . . 45
6.1. The WWW-Authenticate Response Header . . . . . . . . . . . 45
6.1.1. The 'realm' Attribute . . . . . . . . . . . . . . . . 46
6.1.2. The 'authorization-uri' Attribute . . . . . . . . . . 46
6.1.3. The 'algorithms' Attribute . . . . . . . . . . . . . . 46
6.1.4. The 'error' Attribute . . . . . . . . . . . . . . . . 46
7. Security Considerations . . . . . . . . . . . . . . . . . . . 46
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 46
Appendix A. Differences from OAuth 1.0a . . . . . . . . . . . . . 46
Appendix B. Document History . . . . . . . . . . . . . . . . . . 47
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 47
10.1. Normative References . . . . . . . . . . . . . . . . . . . 47
10.2. Informative References . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 48
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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 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).
The use of OAuth with any other transport protocol than HTTP
[RFC2616] (or HTTP over TLS 1.0 as defined by [RFC2818] is undefined.
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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.
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.
authorization endpoint
The authorization server's HTTP endpoint capable of
authenticating the resource owner 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.
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
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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 where the
client is acting on behalf of an end user, end user credentials flows
where the client uses the end user's credentials directly to obtain
authorization, and autonomous flows where the client is acting for
itself (the client is also the resource owner).
Additional authorization flows may be defined by other specifications
to cover different scenarios and client types.
The user delegation authorization 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), and therefore cannot
receive incoming requests from the authorization server. This
flow is described in Section 3.5.1.
o Web Server Flow - This flow is optimized for cases where the
client is capable of receiving incoming HTTP requests (act as an
HTTP server). This flow is described in Section 3.5.2.
o Device Flow - This flow 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 3.5.3.
The end user credentials flow defined by this specification is:
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
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and password. This flow is described in Section 3.6.1.
The autonomous authorization flows defined by this specifications
are:
o Client Credentials Flow - The client uses its credentials to
obtain an access token. This flow is described in Section 3.7.1.
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 3.7.2.
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."
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.
When issuing an access token, the scope, duration, and other access
attributes granted by the resource owner must be retained and
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enforced by the resource server when receiving a protected resource
request and by the authorization server when receiving a token
refresh request made with the access token issued.
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. Authorization Endpoint
Clients direct the resource owner to the authorization endpoint to
approve their access request. Before granting access, the resource
owner first authenticate with the authorization server. 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 authorization 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 auth-uri (Section 6.1.2) attribute).
The authorization endpoint advertised by the resource server MAY
include a query components as defined by [RFC3986] section 3.
Since requests to the authorization 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 or SSL (or a secure channel with equivalent
protections) when sending requests to the authorization endpoints.
3.2. 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"
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response header token-uri (Section 6.1.2) attribute).
The token endpoint advertised by the resource server MAY include a
query components 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 or SSL (or a secure channel with equivalent
protections) when sending requests to the token endpoints.
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. Flow Parameters
Clients should avoid making assumptions about the size of tokens and
other values received from the authorization server, which are left
undefined by this specification. Servers should document the
expected size of any value they issue.
3.4. Client Credentials
When requesting access from the authorization server, the client
identifies itself using its authorization-server-issued 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 the client incapable or
keeping their secrets confidential.
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3.5. User Delegation Flows
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.
3.5.1. 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. The client is
capable of interacting with the end user's user-agent but is
incapable of receiving incoming requests from the authorization
server (incapable of acting as an HTTP server).
Instead of receiving incoming requests, 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
client is incapable of receiving incoming requests, the access token
is encoded into the redirection URI which exposes it 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 | +----------------+
+----------+
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Figure 3
The user-agent flow illustrated in Figure 3 includes the following
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.
3.5.1.1. 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 user authorization endpoint URI:
type
REQUIRED. The parameter value MUST be set to "user_agent"
(case sensitive).
client_id
REQUIRED. The client identifier as described in Section 3.4.
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
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completed. The authorization server SOULD require the client
to pre-register their redirection URI. The redirection URI
MUST NOT includes a query component as defined by [RFC3986]
section 3 if the "state" parameter is present.
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.
immediate
OPTIONAL. The parameter value must be set to "true" or "false"
(case sensitive). 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
redirection URI received matches the registered URI associated with
the client identifier.
The authorization server authenticates the end user and obtains an
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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.
3.5.1.1.1. 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
3.5.1.1.2. 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:
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error
REQUIRED. The parameter value MUST be set to "user_denied"
(case sensitive).
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 3.5.1.2.
3.5.1.2. 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.
3.5.2. 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).
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+----------+ 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 authorization 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.
(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.
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(E) The authorization server validates the client credentials and
the verification code and responds back with the access token.
3.5.2.1. 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 user authorization endpoint URI:
type
REQUIRED. The parameter value MUST be set to "web_server"
(case sensitive).
client_id
REQUIRED. The client identifier as described in Section 3.4.
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. The redirection URI MUST
NOT includes a query component as defined by [RFC3986] section
3 if the "state" parameter is present.
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.
immediate
OPTIONAL. The parameter value must be set to "true" or "false"
(case sensitive). 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
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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.
3.5.2.1.1. 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:
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
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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
3.5.2.1.2. 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"
(case sensitive).
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
The authorization flow concludes unsuccessfully.
3.5.2.2. 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"
(case sensitive).
client_id
REQUIRED. The client identifier as described in Section 3.4.
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client_secret
REQUIRED if the client identifier has a matching secret. The
client secret as described in Section 3.4.
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.
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
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 an access token and delivers it to the
client in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 200 status code (OK).
The response contains the following parameters:
access_token
REQUIRED. The access token issued by the authorization server.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime.
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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.
For example:
HTTP/1.1 200 OK
Content-Type: application/x-www-form-urlencoded
access_token=SlAV32hkKG&expires_in=3600&refresh_token=8xLOxBtZp8
If the request is invalid, the authorization server returns an error
message in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 400 status code (Bad Request).
The response contains the following parameter:
error
OPTIONAL. The parameter value MUST be set to either
"redirect_uri_mismatch" or "expired_verification_code" (case
sensitive).
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/x-www-form-urlencoded
error=expired_verification_code
3.5.3. 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.
home computer, a laptop, or a smartphone). 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
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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:
(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, a user
code, and provides the end user authorization URI.
(C) The client instructs the end user to use its user-agent
(elsewhere) and visit the provided authorization URI. The
client provides the user with the user code to enter in order to
grant access.
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(D) The authorization server authenticates the end user (via the
user-agent) and prompts the end user to grant the client's
access request by entering the user code provided by the client.
(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 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.
3.5.3.1. Client Requests Authorization
The client initiates the flow by requesting a set of verification
codes from the authorization server by making an HTTP "GET" request
to the authorization 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' (case
sensitive).
client_id
REQUIRED. The client identifier as described in Section 3.4.
For example, the client makes the following HTTPS request (line
breaks are for display purposes only):
GET /authorize?type=device&client_id=s6BhdRkqt3
HTTP/1.1
Host: server.example.com
In response, the authorization server generates a verification code
and a user code and includes them in the HTTP response body using the
"application/x-www-form-urlencoded" format as defined by
[W3C.REC-html40-19980424] with a 200 status code (OK). The response
contains the following parameters:
code
REQUIRED. The verification code.
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user_code
REQUIRED. The user code.
user_uri
REQUIRED. The user authorization URI on the authorization
server.
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.
For example (line breaks are for display purposes only):
HTTP/1.1 200 OK
Content-Type: application/x-www-form-urlencoded
device_code=74tq5miHKB&user_code=94248&user_uri=http%3A%2F%2
Fwww%2Eexample%2Ecom%2Fdevice&interval=5
The client displays the user code and the user authorization URI to
the end-user, and instructs the end user to visit the URI using a
user-agent and enter the user code.
The end user manually types the provided URI and authenticates with
the authorization server. The authorization server prompts the end
user to authorize the client's request by entering the 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.
3.5.3.2. 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.
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The client requests an access token by making an HTTP "GET" 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' (case
sensitive).
client_id
REQUIRED. The client identifier as described in Section 3.4.
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.
For example, the client makes the following HTTPS request (line
breaks are for display purposes only):
GET /token?type=device&client_id=s6BhdRkqt3
&code=J2vC42OifV HTTP/1.1
Host: server.example.com
3.5.3.2.1. End User Grants Authorization
If the end user authorized the request, the authorization server
issues an access token and delivers it to the client by including it
in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 200 status code (OK). The response
contains the following parameters:
access_token
REQUIRED. The access token.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime.
refresh_token
OPTIONAL. The refresh token.
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access_token_secret
REQUIRED if requested by the client. The corresponding access
token secret as requested by the client.
For example:
HTTP/1.1 200 OK
Content-Type: application/x-www-form-urlencoded
access_token=FJQbwq9OD8&expires_in=3600
3.5.3.2.2. End User Denies Authorization
If the end user denied the request, the authorization server provides
the client with the error message in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 400 status code (Bad Request). The
response contains the following parameters:
error
REQUIRED. Value must be set to "authorization_declined".
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/x-www-form-urlencoded
error=authorization_declined
3.5.3.2.3. End User Authorization Pending or Expired
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 provides the
client with the error message in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 400 status code (Bad Request). The
response contains the following parameters:
error
REQUIRED. Value MUST be set to "authorization_pending",
"slow_down", or "code_expired" (case sensitive).
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For example:
HTTP/1.1 400 Bad Request
Content-Type: application/x-www-form-urlencoded
error=authorization_pending
3.6. End User Credentials Flows
End user credential flows are used to grant client access to
protected resources by the end user directly sharing the end user
credentials (typically a username and password) with the client.
Unlike user delegation flows, end user credentials flows require a
much higher degree of trust between the client and end user.
These flows are 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 user credentials flows, and
SHOULD only do so when other delegation flows are not viable.
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.
3.6.1. Username and Password Flow
The username and password flow is an end user credentials flow
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.
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.
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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.
3.6.1.1. 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' (case
sensitive).
client_id
REQUIRED. The client identifier as described in Section 3.4.
client_secret
REQUIRED. The client secret as described in Section 3.4.
OPTIONAL if no client secret was issued.
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username
REQUIRED. The end user's username.
password
REQUIRED. The end user's password.
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.
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 issue an access token and deliver to
the client in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 200 status code (OK).
The response contains the following parameters:
access_token
REQUIRED. The access token.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime.
refresh_token
OPTIONAL. The refresh token.
access_token_secret
REQUIRED if requested by the client. The corresponding access
token secret as requested by the client.
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For example:
HTTP/1.1 200 OK
Content-Type: application/x-www-form-urlencoded
access_token=FJQbwq9OD8&refresh_token=gO3CHNqpH8
If the request is invalid, the authorization server returns an error
message in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 400 status code (Bad Request).
The response contains the following parameter:
error
OPTIONAL. The parameter value MUST be set to either
"incorrect_credentials" or "unauthorized_client" (case
sensitive).
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/x-www-form-urlencoded
error=incorrect_credentials
3.7. Autonomous Client Flows
Autonomous client flows are used to grant client access to protected
resources controlled by the client (i.e. the client is the resource
owner). For example, these flows are useful when a service provides
both client-specific resources in addition to end user resources.
3.7.1. Client Credentials Flow
The client credentials flow is used when the client acts autonomously
without acting on behalf of a separate resource owner. The client
secret is assumed to be high-entropy since it is not designed to be
memorize by an end user.
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+--------+ +---------------+
| | | |
| |>--(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.
3.7.1.1. 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_cred'
(case sensitive).
client_id
REQUIRED. The client identifier as described in Section 3.4.
client_secret
REQUIRED. The client secret as described in Section 3.4.
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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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=client_cred&client_id=s6BhdRkqt3&client_secret=47HDu8s
The authorization server MUST validate the client credentials and if
valid issue an access token and deliver to the client in the HTTP
response body using the "application/x-www-form-urlencoded" content
type as defined by [W3C.REC-html40-19980424] with a 200 status code
(OK).
The response contains the following parameters:
access_token
REQUIRED. The access token.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime.
refresh_token
OPTIONAL. The refresh token.
access_token_secret
REQUIRED if requested by the client. The corresponding access
token secret as requested by the client.
For example:
HTTP/1.1 200 OK
Content-Type: application/x-www-form-urlencoded
access_token=FJQbwq9OD8
If the request is invalid, the authorization server returns an error
message in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 400 status code (Bad Request).
The response contains the following parameter:
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error
OPTIONAL. The parameter value MUST be set to either
"incorrect_credentials" or "unauthorized_client" (case
sensitive).
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/x-www-form-urlencoded
error=incorrect_credentials
3.7.2. Assertion Flow
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
prior to initiating the flow. The process in which the assertion is
obtained is defined by the assertion issuer and the authorization
server, and is beyond the scope of this specification.
The client credentials flow is used when the client acts autonomously
without acting on behalf of a separate resource owner.
+--------+ +---------------+
| | | |
| |>--(A)------ Assertion ---------->| Authorization |
| Client | | Server |
| |<--(B)---- Access Token ---------<| |
| | (w/ Optional Refresh Token) | |
+--------+ +---------------+
Figure 8
The client credential flow illustrated in Figure 8 includes the
following steps:
(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.
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3.7.2.1. 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' (case
sensitive).
format
REQUIRED. The format of the assertion as defined by the
authorization server.
assertion
REQUIRED. The assertion.
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.
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
issue an access token and deliver to the client in the HTTP response
body using the "application/x-www-form-urlencoded" content type as
defined by [W3C.REC-html40-19980424] with a 200 status code (OK).
The response contains the following parameters:
access_token
REQUIRED. The access token.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime.
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refresh_token
OPTIONAL. The refresh token.
access_token_secret
REQUIRED if requested by the client. The corresponding access
token secret as requested by the client.
For example:
HTTP/1.1 200 OK
Content-Type: application/x-www-form-urlencoded
access_token=FJQbwq9OD8
If the assertion is invalid, the authorization server returns an
error message in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 400 status code (Bad Request).
The response contains the following parameter:
error
OPTIONAL. The parameter value MUST be set to either
"invalid_assertion" or "unknown_format" (case sensitive).
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/x-www-form-urlencoded
error=incorrect_credentials
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).
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+--------+ 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' (case
sensitive).
client_id
REQUIRED. The client identifier as described in Section 3.4.
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.
For example, the client makes the following HTTPS request (line break
are for display purposes only):
POST /authorize 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
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The authorization server MUST 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 a new access token and includes the
following parameters in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 200 status code (OK):
access_token
REQUIRED. The access token.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime.
access_token_secret
REQUIRED if requested by the client. The corresponding access
token secret as requested by the client.
For example:
HTTP/1.1 200 OK
Content-Type: application/x-www-form-urlencoded
access_token=8F44J2HGMl&access_token_secret=hfd83hjd&expires_in=3600
If the request fails verification, the authorization server returns
an error message in the HTTP response body using the
"application/x-www-form-urlencoded" content type as defined by
[W3C.REC-html40-19980424] with a 400 status code (Bad Request).
The response contains the following parameter:
error
OPTIONAL. The parameter value MUST be set to either
"incorrect_credentials", "authorization_expired", or
"unsupported_secret_type" (case sensitive).
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/x-www-form-urlencoded
error=incorrect_credentials
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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 matchin secret by specifying the desired secret type
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 must 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
SSL/TLS).
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.
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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.
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 <">
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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"
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
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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 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
"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 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.
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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 matchin "hmac-sha256" secret by using
the "token_type" parameter when requesting an access token.
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
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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.
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.
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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
without using additional protections such as SSL/TLS.
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:
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text
is set to the value of the normalize request string as
described in Section 5.3.1.2.
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
authorization 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 authorization 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 HTTP status code
(Unauthorized), and includes 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 authz-uri ]
[ CS token-uri ]
[ CS algorithms ]
[ CS error ]
authz-uri = "auth-uri" "=" URI-Reference
token-uri = "token-uri" "=" URI-Reference
algorithms = "algorithms" "=" <"> 1#algorithm-name <">
error = "error" "=" <"> token <">
CS = OWS "," OWS
6.1.1. The 'realm' Attribute
The "realm" attribute is used to provide the protected resources
partition as defined by [RFC2617].
6.1.2. The 'authorization-uri' Attribute
6.1.3. The 'algorithms' Attribute
6.1.4. The 'error' Attribute
7. Security Considerations
[[ Todo ]]
8. IANA Considerations
[[ Not Yet ]]
9. Acknowledgements
[[ Add OAuth 1.0a authors + WG contributors ]]
Appendix A. Differences from OAuth 1.0a
[[ Todo ]]
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Appendix B. Document History
[[ to be removed by RFC editor before publication as an RFC ]]
-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
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.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
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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.
[W3C.REC-html40-19980424]
Hors, A., Jacobs, I., and D. Raggett, "HTML 4.0
Specification", World Wide Web Consortium
Recommendation REC-html40-19980424, April 1998,
<http://www.w3.org/TR/1998/REC-html40-19980424>.
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
David Recordon
Facebook
Email: davidrecordon@facebook.com
URI: http://www.davidrecordon.com/
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Dick Hardt
Email: dick.hardt@gmail.com
URI: http://dickhardt.org/
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