RFC 6749
The OAuth 2.0 Authorization Framework
Pages: 76
Proposed Standard
→ Errata
Obsoletes: 5849
Updated by: 8252 8996
Proposed Standard
→ Errata
Obsoletes: 5849
Updated by: 8252 8996
Part 1 of 4 – Pages 1 to 13
Internet Engineering Task Force (IETF) D. Hardt, Ed. Request for Comments: 6749 Microsoft Obsoletes: 5849 October 2012 Category: Standards Track ISSN: 2070-1721 The OAuth 2.0 Authorization FrameworkAbstract
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. This document is a product of the Internet Engineering Task Force (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. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6749. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................4 1.1. Roles ......................................................6 1.2. Protocol Flow ..............................................7 1.3. Authorization Grant ........................................8 1.3.1. Authorization Code ..................................8 1.3.2. Implicit ............................................8 1.3.3. Resource Owner Password Credentials .................9 1.3.4. Client Credentials ..................................9 1.4. Access Token ..............................................10 1.5. Refresh Token .............................................10 1.6. TLS Version ...............................................12 1.7. HTTP Redirections .........................................12 1.8. Interoperability ..........................................12 1.9. Notational Conventions ....................................13 2. Client Registration ............................................13 2.1. Client Types ..............................................14 2.2. Client Identifier .........................................15 2.3. Client Authentication .....................................16 2.3.1. Client Password ....................................16 2.3.2. Other Authentication Methods .......................17 2.4. Unregistered Clients ......................................17 3. Protocol Endpoints .............................................18 3.1. Authorization Endpoint ....................................18 3.1.1. Response Type ......................................19 3.1.2. Redirection Endpoint ...............................19 3.2. Token Endpoint ............................................21 3.2.1. Client Authentication ..............................22 3.3. Access Token Scope ........................................23 4. Obtaining Authorization ........................................23 4.1. Authorization Code Grant ..................................24 4.1.1. Authorization Request ..............................25 4.1.2. Authorization Response .............................26 4.1.3. Access Token Request ...............................29 4.1.4. Access Token Response ..............................30 4.2. Implicit Grant ............................................31 4.2.1. Authorization Request ..............................33 4.2.2. Access Token Response ..............................35 4.3. Resource Owner Password Credentials Grant .................37 4.3.1. Authorization Request and Response .................39 4.3.2. Access Token Request ...............................39 4.3.3. Access Token Response ..............................40 4.4. Client Credentials Grant ..................................40 4.4.1. Authorization Request and Response .................41 4.4.2. Access Token Request ...............................41 4.4.3. Access Token Response ..............................42 4.5. Extension Grants ..........................................42
5. Issuing an Access Token ........................................43 5.1. Successful Response .......................................43 5.2. Error Response ............................................45 6. Refreshing an Access Token .....................................47 7. Accessing Protected Resources ..................................48 7.1. Access Token Types ........................................49 7.2. Error Response ............................................49 8. Extensibility ..................................................50 8.1. Defining Access Token Types ...............................50 8.2. Defining New Endpoint Parameters ..........................50 8.3. Defining New Authorization Grant Types ....................51 8.4. Defining New Authorization Endpoint Response Types ........51 8.5. Defining Additional Error Codes ...........................51 9. Native Applications ............................................52 10. Security Considerations .......................................53 10.1. Client Authentication ....................................53 10.2. Client Impersonation .....................................54 10.3. Access Tokens ............................................55 10.4. Refresh Tokens ...........................................55 10.5. Authorization Codes ......................................56 10.6. Authorization Code Redirection URI Manipulation ..........56 10.7. Resource Owner Password Credentials ......................57 10.8. Request Confidentiality ..................................58 10.9. Ensuring Endpoint Authenticity ...........................58 10.10. Credentials-Guessing Attacks ............................58 10.11. Phishing Attacks ........................................58 10.12. Cross-Site Request Forgery ..............................59 10.13. Clickjacking ............................................60 10.14. Code Injection and Input Validation .....................60 10.15. Open Redirectors ........................................60 10.16. Misuse of Access Token to Impersonate Resource Owner in Implicit Flow ..................................61 11. IANA Considerations ...........................................62 11.1. OAuth Access Token Types Registry ........................62 11.1.1. Registration Template .............................62 11.2. OAuth Parameters Registry ................................63 11.2.1. Registration Template .............................63 11.2.2. Initial Registry Contents .........................64 11.3. OAuth Authorization Endpoint Response Types Registry .....66 11.3.1. Registration Template .............................66 11.3.2. Initial Registry Contents .........................67 11.4. OAuth Extensions Error Registry ..........................67 11.4.1. Registration Template .............................68 12. References ....................................................68 12.1. Normative References .....................................68 12.2. Informative References ...................................70
Appendix A. Augmented Backus-Naur Form (ABNF) Syntax ..............71 A.1. "client_id" Syntax ........................................71 A.2. "client_secret" Syntax ....................................71 A.3. "response_type" Syntax ....................................71 A.4. "scope" Syntax ............................................72 A.5. "state" Syntax ............................................72 A.6. "redirect_uri" Syntax .....................................72 A.7. "error" Syntax ............................................72 A.8. "error_description" Syntax ................................72 A.9. "error_uri" Syntax ........................................72 A.10. "grant_type" Syntax .......................................73 A.11. "code" Syntax .............................................73 A.12. "access_token" Syntax .....................................73 A.13. "token_type" Syntax .......................................73 A.14. "expires_in" Syntax .......................................73 A.15. "username" Syntax .........................................73 A.16. "password" Syntax .........................................73 A.17. "refresh_token" Syntax ....................................74 A.18. Endpoint Parameter Syntax .................................74 Appendix B. Use of application/x-www-form-urlencoded Media Type ...74 Appendix 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 clear-text. 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 resources. 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
password.
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
owner.
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.
1.1. Roles
OAuth defines four roles: resource owner An entity capable of granting access to a protected resource. When the resource owner is a person, it is referred to as an end-user. resource server The server hosting the protected resources, capable of accepting and responding to protected resource requests using access tokens. client 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 devices). authorization server 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 authorization server. (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.
1.3.2. Implicit
The implicit grant is a simplified authorization code flow optimized
for clients implemented in a browser using a scripting language such
as JavaScript. In the implicit flow, instead of issuing the client
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 authorization server.
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 server. 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 as [RFC6750].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 Figure 1). 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.
1.8. Interoperability
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
implementations.
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" [RFC3986]. 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.
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