Internet Engineering Task Force (IETF) D. Hardt, Ed.
Request for Comments: 6749 Microsoft
Obsoletes: 5849 October 2012
Category: Standards Track
The OAuth 2.0 Authorization Framework
The OAuth 2.0 authorization framework enables a third-party
application to obtain limited access to an HTTP service, either on
behalf of a resource owner by orchestrating an approval interaction
between the resource owner and the HTTP service, or by allowing the
third-party application to obtain access on its own behalf. This
specification replaces and obsoletes the OAuth 1.0 protocol described
in RFC 5849.
Status of This Memo
This is an Internet Standards Track document.
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(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
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Appendix A. Augmented Backus-Naur Form (ABNF) Syntax ..............71A.1. "client_id" Syntax ........................................71A.2. "client_secret" Syntax ....................................71A.3. "response_type" Syntax ....................................71A.4. "scope" Syntax ............................................72A.5. "state" Syntax ............................................72A.6. "redirect_uri" Syntax .....................................72A.7. "error" Syntax ............................................72A.8. "error_description" Syntax ................................72A.9. "error_uri" Syntax ........................................72A.10. "grant_type" Syntax .......................................73A.11. "code" Syntax .............................................73A.12. "access_token" Syntax .....................................73A.13. "token_type" Syntax .......................................73A.14. "expires_in" Syntax .......................................73A.15. "username" Syntax .........................................73A.16. "password" Syntax .........................................73A.17. "refresh_token" Syntax ....................................74A.18. Endpoint Parameter Syntax .................................74Appendix B. Use of application/x-www-form-urlencoded Media Type ...74Appendix C. Acknowledgements ......................................751. Introduction
In the traditional client-server authentication model, the client
requests an access-restricted resource (protected resource) on the
server by authenticating with the server using the resource owner's
credentials. In order to provide third-party applications access to
restricted resources, the resource owner shares its credentials with
the third party. This creates several problems and limitations:
o Third-party applications are required to store the resource
owner's credentials for future use, typically a password in
o Servers are required to support password authentication, despite
the security weaknesses inherent in passwords.
o Third-party applications gain overly broad access to the resource
owner's protected resources, leaving resource owners without any
ability to restrict duration or access to a limited subset of
o Resource owners cannot revoke access to an individual third party
without revoking access to all third parties, and must do so by
changing the third party's password.
o Compromise of any third-party application results in compromise of
the end-user's password and all of the data protected by that
OAuth addresses these issues by introducing an authorization layer
and separating the role of the client from that of the resource
owner. In OAuth, the client requests access to resources controlled
by the resource owner and hosted by the resource server, and is
issued a different set of credentials than those of the resource
Instead of using the resource owner's credentials to access protected
resources, the client obtains an access token -- a string denoting a
specific scope, lifetime, and other access attributes. Access tokens
are issued to third-party clients by an authorization server with the
approval of the resource owner. The client uses the access token to
access the protected resources hosted by the resource server.
For example, an end-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 a server trusted by the photo-sharing service
(authorization server), which issues the printing service delegation-
specific credentials (access token).
This specification is designed for use with HTTP ([RFC2616]). The
use of OAuth over any protocol other than HTTP is out of scope.
The OAuth 1.0 protocol ([RFC5849]), published as an informational
document, was the result of a small ad hoc community effort. This
Standards Track specification builds on the OAuth 1.0 deployment
experience, as well as additional use cases and extensibility
requirements gathered from the wider IETF community. The OAuth 2.0
protocol is not backward compatible with OAuth 1.0. The two versions
may co-exist on the network, and implementations may choose to
support both. However, it is the intention of this specification
that new implementations support OAuth 2.0 as specified in this
document and that OAuth 1.0 is used only to support existing
deployments. The OAuth 2.0 protocol shares very few implementation
details with the OAuth 1.0 protocol. Implementers familiar with
OAuth 1.0 should approach this document without any assumptions as to
its structure and details.
OAuth defines four roles:
An entity capable of granting access to a protected resource.
When the resource owner is a person, it is referred to as an
The server hosting the protected resources, capable of accepting
and responding to protected resource requests using access tokens.
An application making protected resource requests on behalf of the
resource owner and with its authorization. The term "client" does
not imply any particular implementation characteristics (e.g.,
whether the application executes on a server, a desktop, or other
The server issuing access tokens to the client after successfully
authenticating the resource owner and obtaining authorization.
The interaction between the authorization server and resource server
is beyond the scope of this specification. The authorization server
may be the same server as the resource server or a separate entity.
A single authorization server may issue access tokens accepted by
multiple resource servers.
1.2. Protocol Flow
| |--(A)- Authorization Request ->| Resource |
| | | Owner |
| |<-(B)-- Authorization Grant ---| |
| | +---------------+
| | +---------------+
| |--(C)-- Authorization Grant -->| Authorization |
| Client | | Server |
| |<-(D)----- Access Token -------| |
| | +---------------+
| | +---------------+
| |--(E)----- Access Token ------>| Resource |
| | | Server |
| |<-(F)--- Protected Resource ---| |
Figure 1: Abstract Protocol Flow
The abstract OAuth 2.0 flow illustrated in Figure 1 describes the
interaction between the four roles and includes the following steps:
(A) The client requests authorization from the resource owner. The
authorization request can be made directly to the resource owner
(as shown), or preferably indirectly via the authorization
server as an intermediary.
(B) The client receives an authorization grant, which is a
credential representing the resource owner's authorization,
expressed using one of four grant types defined in this
specification or using an extension grant type. The
authorization grant type depends on the method used by the
client to request authorization and the types supported by the
(C) The client requests an access token by authenticating with the
authorization server and presenting the authorization grant.
(D) The authorization server authenticates the client and validates
the authorization grant, and if valid, issues an access token.
(E) The client requests the protected resource from the resource
server and authenticates by presenting the access token.
(F) The resource server validates the access token, and if valid,
serves the request.
The preferred method for the client to obtain an authorization grant
from the resource owner (depicted in steps (A) and (B)) is to use the
authorization server as an intermediary, which is illustrated in
Figure 3 in Section 4.1.
1.3. Authorization Grant
An authorization grant is a credential representing the resource
owner's authorization (to access its protected resources) used by the
client to obtain an access token. This specification defines four
grant types -- authorization code, implicit, resource owner password
credentials, and client credentials -- as well as an extensibility
mechanism for defining additional types.
1.3.1. Authorization Code
The authorization code is obtained by using an authorization server
as an intermediary between the client and resource owner. Instead of
requesting authorization directly from the resource owner, the client
directs the resource owner to an authorization server (via its
user-agent as defined in [RFC2616]), which in turn directs the
resource owner back to the client with the authorization code.
Before directing the resource owner back to the client with the
authorization code, the authorization server authenticates the
resource owner and obtains authorization. Because the resource owner
only authenticates with the authorization server, the resource
owner's credentials are never shared with the client.
The authorization code provides a few important security benefits,
such as the ability to authenticate the client, as well as the
transmission of the access token directly to the client without
passing it through the resource owner's user-agent and potentially
exposing it to others, including the resource owner.
The implicit grant is a simplified authorization code flow optimized
for clients implemented in a browser using a scripting language such
an authorization code, the client is issued an access token directly
(as the result of the resource owner authorization). The grant type
is implicit, as no intermediate credentials (such as an authorization
code) are issued (and later used to obtain an access token).
When issuing an access token during the implicit grant flow, the
authorization server does not authenticate the client. In some
cases, the client identity can be verified via the redirection URI
used to deliver the access token to the client. The access token may
be exposed to the resource owner or other applications with access to
the resource owner's user-agent.
Implicit grants improve the responsiveness and efficiency of some
clients (such as a client implemented as an in-browser application),
since it reduces the number of round trips required to obtain an
access token. However, this convenience should be weighed against
the security implications of using implicit grants, such as those
described in Sections 10.3 and 10.16, especially when the
authorization code grant type is available.
1.3.3. Resource Owner Password Credentials
The resource owner password credentials (i.e., username and password)
can be used directly as an authorization grant to obtain an access
token. The credentials should only be used when there is a high
degree of trust between the resource owner and the client (e.g., the
client is part of the device operating system or a highly privileged
application), and when other authorization grant types are not
available (such as an authorization code).
Even though this grant type requires direct client access to the
resource owner credentials, the resource owner credentials are used
for a single request and are exchanged for an access token. This
grant type can eliminate the need for the client to store the
resource owner credentials for future use, by exchanging the
credentials with a long-lived access token or refresh token.
1.3.4. Client Credentials
The client credentials (or other forms of client authentication) can
be used as an authorization grant when the authorization scope is
limited to the protected resources under the control of the client,
or to protected resources previously arranged with the authorization
server. Client credentials are used as an authorization grant
typically when the client is acting on its own behalf (the client is
also the resource owner) or is requesting access to protected
resources based on an authorization previously arranged with the
1.4. Access Token
Access tokens are credentials used to access protected resources. An
access token is a string representing an authorization issued to the
client. The string is usually opaque to the client. Tokens
represent specific scopes and durations of access, granted by the
resource owner, and enforced by the resource server and authorization
The token may denote an identifier used to retrieve the authorization
information or may self-contain the authorization information in a
verifiable manner (i.e., a token string consisting of some data and a
signature). Additional authentication credentials, which are beyond
the scope of this specification, may be required in order for the
client to use a token.
The access token provides an abstraction layer, replacing different
authorization constructs (e.g., username and password) with a single
token understood by the resource server. This abstraction enables
issuing access tokens more restrictive than the authorization grant
used to obtain them, as well as removing the resource server's need
to understand a wide range of authentication methods.
Access tokens can have different formats, structures, and methods of
utilization (e.g., cryptographic properties) based on the resource
server security requirements. Access token attributes and the
methods used to access protected resources are beyond the scope of
this specification and are defined by companion specifications such
1.5. Refresh Token
Refresh tokens are credentials used to obtain access tokens. Refresh
tokens are issued to the client by the authorization server and are
used to obtain a new access token when the current access token
becomes invalid or expires, or to obtain additional access tokens
with identical or narrower scope (access tokens may have a shorter
lifetime and fewer permissions than authorized by the resource
owner). Issuing a refresh token is optional at the discretion of the
authorization server. If the authorization server issues a refresh
token, it is included when issuing an access token (i.e., step (D) in
A refresh token is a string representing the authorization granted to
the client by the resource owner. The string is usually opaque to
the client. The token denotes an identifier used to retrieve the
authorization information. Unlike access tokens, refresh tokens are
intended for use only with authorization servers and are never sent
to resource servers.
| |--(A)------- Authorization Grant --------->| |
| | | |
| |<-(B)----------- Access Token -------------| |
| | & Refresh Token | |
| | | |
| | +----------+ | |
| |--(C)---- Access Token ---->| | | |
| | | | | |
| |<-(D)- Protected Resource --| Resource | | Authorization |
| Client | | Server | | Server |
| |--(E)---- Access Token ---->| | | |
| | | | | |
| |<-(F)- Invalid Token Error -| | | |
| | +----------+ | |
| | | |
| |--(G)----------- Refresh Token ----------->| |
| | | |
| |<-(H)----------- Access Token -------------| |
+--------+ & Optional Refresh Token +---------------+
Figure 2: Refreshing an Expired Access Token
The flow illustrated in Figure 2 includes the following steps:
(A) The client requests an access token by authenticating with the
authorization server and presenting an authorization grant.
(B) The authorization server authenticates the client and validates
the authorization grant, and if valid, issues an access token
and a refresh token.
(C) The client makes a protected resource request to the resource
server by presenting the access token.
(D) The resource server validates the access token, and if valid,
serves the request.
(E) Steps (C) and (D) repeat until the access token expires. If the
client knows the access token expired, it skips to step (G);
otherwise, it makes another protected resource request.
(F) Since the access token is invalid, the resource server returns
an invalid token error.
(G) The client requests a new access token by authenticating with
the authorization server and presenting the refresh token. The
client authentication requirements are based on the client type
and on the authorization server policies.
(H) The authorization server authenticates the client and validates
the refresh token, and if valid, issues a new access token (and,
optionally, a new refresh token).
Steps (C), (D), (E), and (F) are outside the scope of this
specification, as described in Section 7.1.6. TLS Version
Whenever Transport Layer Security (TLS) is used by this
specification, the appropriate version (or versions) of TLS will vary
over time, based on the widespread deployment and known security
vulnerabilities. At the time of this writing, TLS version 1.2
[RFC5246] is the most recent version, but has a very limited
deployment base and might not be readily available for
implementation. TLS version 1.0 [RFC2246] is the most widely
deployed version and will provide the broadest interoperability.
Implementations MAY also support additional transport-layer security
mechanisms that meet their security requirements.
1.7. HTTP Redirections
This specification makes extensive use of HTTP redirections, in which
the client or the authorization server directs the resource owner's
user-agent to another destination. While the examples in this
specification show the use of the HTTP 302 status code, any other
method available via the user-agent to accomplish this redirection is
allowed and is considered to be an implementation detail.
OAuth 2.0 provides a rich authorization framework with well-defined
security properties. However, as a rich and highly extensible
framework with many optional components, on its own, this
specification is likely to produce a wide range of non-interoperable
In addition, this specification leaves a few required components
partially or fully undefined (e.g., client registration,
authorization server capabilities, endpoint discovery). Without
these components, clients must be manually and specifically
configured against a specific authorization server and resource
server in order to interoperate.
This framework was designed with the clear expectation that future
work will define prescriptive profiles and extensions necessary to
achieve full web-scale interoperability.
1.9. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
specification are to be interpreted as described in [RFC2119].
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234]. Additionally, the rule URI-reference is
included from "Uniform Resource Identifier (URI): Generic Syntax"
Certain security-related terms are to be understood in the sense
defined in [RFC4949]. These terms include, but are not limited to,
"attack", "authentication", "authorization", "certificate",
"confidentiality", "credential", "encryption", "identity", "sign",
"signature", "trust", "validate", and "verify".
Unless otherwise noted, all the protocol parameter names and values
are case sensitive.