Network Working Group D. Hardt
Internet-Draft SignIn.Org
Intended status: Standards Track A. Parecki
Expires: 8 September 2020 Okta
T. Lodderstedt
yes.com
7 March 2020
The OAuth 2.1 Authorization Framework
draft-parecki-oauth-v2-1-00
Abstract
The OAuth 2.1 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 2.0 Authorization
Framework described in RFC 6749.
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 https://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 8 September 2020.
Copyright Notice
Copyright (c) 2020 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 (https://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
Hardt, et al. Expires 8 September 2020 [Page 1]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
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 . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Authorization Grant . . . . . . . . . . . . . . . . . . . 8
1.3.1. Authorization Code . . . . . . . . . . . . . . . . . 8
1.3.2. Client Credentials . . . . . . . . . . . . . . . . . 8
1.4. Access Token . . . . . . . . . . . . . . . . . . . . . . 9
1.5. Refresh Token . . . . . . . . . . . . . . . . . . . . . . 9
1.6. TLS Version . . . . . . . . . . . . . . . . . . . . . . . 11
1.7. HTTP Redirections . . . . . . . . . . . . . . . . . . . . 11
1.8. Interoperability . . . . . . . . . . . . . . . . . . . . 11
1.9. Notational Conventions . . . . . . . . . . . . . . . . . 12
2. Client Registration . . . . . . . . . . . . . . . . . . . . . 12
2.1. Client Types . . . . . . . . . . . . . . . . . . . . . . 13
2.2. Client Identifier . . . . . . . . . . . . . . . . . . . . 14
2.3. Client Authentication . . . . . . . . . . . . . . . . . . 14
2.3.1. Client Password . . . . . . . . . . . . . . . . . . . 15
2.3.2. Other Authorization Methods . . . . . . . . . . . . . 16
2.4. Unregistered Clients . . . . . . . . . . . . . . . . . . 16
3. Protocol Endpoints . . . . . . . . . . . . . . . . . . . . . 16
3.1. Authorization Endpoint . . . . . . . . . . . . . . . . . 17
3.1.1. Response Type . . . . . . . . . . . . . . . . . . . . 17
3.1.2. Redirection Endpoint . . . . . . . . . . . . . . . . 18
3.2. Token Endpoint . . . . . . . . . . . . . . . . . . . . . 20
3.2.1. Client Authentication . . . . . . . . . . . . . . . . 20
3.3. Access Token Scope . . . . . . . . . . . . . . . . . . . 21
4. Obtaining Authorization . . . . . . . . . . . . . . . . . . . 22
4.1. Authorization Code Grant . . . . . . . . . . . . . . . . 22
4.1.1. Authorization Request . . . . . . . . . . . . . . . . 23
4.1.2. Authorization Response . . . . . . . . . . . . . . . 26
4.1.3. Access Token Request . . . . . . . . . . . . . . . . 29
4.1.4. Access Token Response . . . . . . . . . . . . . . . . 30
4.2. Client Credentials Grant . . . . . . . . . . . . . . . . 30
4.2.1. Authorization Request and Response . . . . . . . . . 31
4.2.2. Access Token Request . . . . . . . . . . . . . . . . 31
4.2.3. Access Token Response . . . . . . . . . . . . . . . . 32
4.3. Extension Grants . . . . . . . . . . . . . . . . . . . . 32
5. Issuing an Access Token . . . . . . . . . . . . . . . . . . . 33
5.1. Successful Response . . . . . . . . . . . . . . . . . . . 33
5.2. Error Response . . . . . . . . . . . . . . . . . . . . . 34
6. Refreshing an Access Token . . . . . . . . . . . . . . . . . 36
Hardt, et al. Expires 8 September 2020 [Page 2]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
7. Accessing Protected Resources . . . . . . . . . . . . . . . . 38
7.1. Access Token Types . . . . . . . . . . . . . . . . . . . 39
7.2. Bearer Tokens . . . . . . . . . . . . . . . . . . . . . . 39
7.2.1. Authenticated Requests . . . . . . . . . . . . . . . 39
7.2.2. The WWW-Authenticate Response Header Field . . . . . 41
7.3. Error Response . . . . . . . . . . . . . . . . . . . . . 43
7.3.1. Error Codes . . . . . . . . . . . . . . . . . . . . . 43
7.4. Access Token Security Considerations . . . . . . . . . . 44
7.4.1. Security Threats . . . . . . . . . . . . . . . . . . 44
7.4.2. Threat Mitigation . . . . . . . . . . . . . . . . . . 45
7.4.3. Summary of Recommendations . . . . . . . . . . . . . 46
7.4.4. Token Replay Prevention . . . . . . . . . . . . . . . 47
7.4.5. Access Token Privilege Restriction . . . . . . . . . 48
8. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 48
8.1. Defining Access Token Types . . . . . . . . . . . . . . . 48
8.2. Defining New Endpoint Parameters . . . . . . . . . . . . 49
8.3. Defining New Authorization Grant Types . . . . . . . . . 49
8.4. Defining New Authorization Endpoint Response Types . . . 49
8.5. Defining Additional Error Codes . . . . . . . . . . . . . 50
9. Security Considerations . . . . . . . . . . . . . . . . . . . 50
9.1. Client Authentication . . . . . . . . . . . . . . . . . . 51
9.1.1. Client Authentication of Native Apps . . . . . . . . 52
9.2. Registration of Native App Clients . . . . . . . . . . . 52
9.3. Client Impersonation . . . . . . . . . . . . . . . . . . 53
9.3.1. Impersonation of Native Apps . . . . . . . . . . . . 53
9.4. Access Tokens . . . . . . . . . . . . . . . . . . . . . . 54
9.4.1. Access Token Privilege Restriction . . . . . . . . . 54
9.4.2. Access Token Replay Prevention . . . . . . . . . . . 54
9.5. Refresh Tokens . . . . . . . . . . . . . . . . . . . . . 55
9.6. Protecting Redirect-Based Flows . . . . . . . . . . . . . 55
9.6.1. Loopback Redirect Considerations in Native Apps . . . 56
9.7. Authorization Codes . . . . . . . . . . . . . . . . . . . 57
9.8. Request Confidentiality . . . . . . . . . . . . . . . . . 58
9.9. Ensuring Endpoint Authenticity . . . . . . . . . . . . . 58
9.10. Credentials-Guessing Attacks . . . . . . . . . . . . . . 58
9.11. Phishing Attacks . . . . . . . . . . . . . . . . . . . . 58
9.12. Fake External User-Agents in Native Apps . . . . . . . . 59
9.13. Malicious External User-Agents in Native Apps . . . . . . 59
9.14. Cross-Site Request Forgery . . . . . . . . . . . . . . . 60
9.15. Clickjacking . . . . . . . . . . . . . . . . . . . . . . 60
9.16. Code Injection and Input Validation . . . . . . . . . . . 61
9.17. Open Redirectors . . . . . . . . . . . . . . . . . . . . 61
9.17.1. Client as Open Redirector . . . . . . . . . . . . . 62
9.17.2. Authorization Server as Open Redirector . . . . . . 62
9.18. Authorization Server Mix-Up Mitigation in Native Apps . . 62
9.19. Embedded User Agents in Native Apps . . . . . . . . . . . 63
9.20. Other Recommendations . . . . . . . . . . . . . . . . . . 64
10. Native Applications . . . . . . . . . . . . . . . . . . . . . 64
Hardt, et al. Expires 8 September 2020 [Page 3]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
10.1. Using Inter-App URI Communication for OAuth in Native
Apps . . . . . . . . . . . . . . . . . . . . . . . . . . 65
10.2. Initiating the Authorization Request from a Native
App . . . . . . . . . . . . . . . . . . . . . . . . . . 65
10.3. Receiving the Authorization Response in a Native App . . 66
10.3.1. Private-Use URI Scheme Redirection . . . . . . . . . 66
10.3.2. Claimed "https" Scheme URI Redirection . . . . . . . 67
10.3.3. Loopback Interface Redirection . . . . . . . . . . . 68
11. Browser-Based Apps . . . . . . . . . . . . . . . . . . . . . 68
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 69
12.1. OAuth Access Token Types Registry . . . . . . . . . . . 69
12.1.1. Registration Template . . . . . . . . . . . . . . . 69
12.1.2. Initial Registry Contents . . . . . . . . . . . . . 70
12.2. OAuth Parameters Registry . . . . . . . . . . . . . . . 70
12.2.1. Registration Template . . . . . . . . . . . . . . . 71
12.2.2. Initial Registry Contents . . . . . . . . . . . . . 71
12.3. OAuth Authorization Endpoint Response Types Registry . . 74
12.3.1. Registration Template . . . . . . . . . . . . . . . 74
12.3.2. Initial Registry Contents . . . . . . . . . . . . . 75
12.4. OAuth Extensions Error Registry . . . . . . . . . . . . 75
12.4.1. Registration Template . . . . . . . . . . . . . . . 75
12.4.2. Initial Registry Contents . . . . . . . . . . . . . 76
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 76
13.1. Normative References . . . . . . . . . . . . . . . . . . 76
13.2. Informative References . . . . . . . . . . . . . . . . . 79
Appendix A. Augmented Backus-Naur Form (ABNF) Syntax . . . . . . 81
A.1. "client_id" Syntax . . . . . . . . . . . . . . . . . . . 82
A.2. "client_secret" Syntax . . . . . . . . . . . . . . . . . 82
A.3. "response_type" Syntax . . . . . . . . . . . . . . . . . 82
A.4. "scope" Syntax . . . . . . . . . . . . . . . . . . . . . 82
A.5. "state" Syntax . . . . . . . . . . . . . . . . . . . . . 82
A.6. "redirect_uri" Syntax . . . . . . . . . . . . . . . . . . 83
A.7. "error" Syntax . . . . . . . . . . . . . . . . . . . . . 83
A.8. "error_description" Syntax . . . . . . . . . . . . . . . 83
A.9. "error_uri" Syntax . . . . . . . . . . . . . . . . . . . 83
A.10. "grant_type" Syntax . . . . . . . . . . . . . . . . . . . 83
A.11. "code" Syntax . . . . . . . . . . . . . . . . . . . . . . 83
A.12. "access_token" Syntax . . . . . . . . . . . . . . . . . . 84
A.13. "token_type" Syntax . . . . . . . . . . . . . . . . . . . 84
A.14. "expires_in" Syntax . . . . . . . . . . . . . . . . . . . 84
A.15. "refresh_token" Syntax . . . . . . . . . . . . . . . . . 84
A.16. Endpoint Parameter Syntax . . . . . . . . . . . . . . . . 84
A.17. "code_verifier" Syntax . . . . . . . . . . . . . . . . . 84
A.18. "code_challenge" Syntax . . . . . . . . . . . . . . . . . 84
Appendix B. Use of application/x-www-form-urlencoded Media
Type . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 85
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 85
Hardt, et al. Expires 8 September 2020 [Page 4]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
1. 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:
* Third-party applications are required to store the resource
owner's credentials for future use, typically a password in clear-
text.
* Servers are required to support password authentication, despite
the security weaknesses inherent in passwords.
* 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.
* 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.
* 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
Hardt, et al. Expires 8 September 2020 [Page 5]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
(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.
Since the publication of the OAuth 2.0 Authorization Framework
([RFC6749]) in October 2012, it has been updated by OAuth 2.0 for
Native Apps ([RFC8252]), OAuth Security Best Current Practice
([I-D.ietf-oauth-security-topics]), and OAuth 2.0 for Browser-Based
Apps ([I-D.ietf-oauth-browser-based-apps]). The OAuth 2.0
Authorization Framework: Bearer Token Usage ([RFC6750]) has also been
updated with ([I-D.ietf-oauth-security-topics]). This Standards
Track specification consolidates the information in all of these
documents and removes features that have been found to be insecure in
[I-D.ietf-oauth-security-topics].
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
Hardt, et al. Expires 8 September 2020 [Page 6]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
+--------+ +---------------+
| |--(1)- Authorization Request ->| Resource |
| | | Owner |
| |<-(2)-- Authorization Grant ---| |
| | +---------------+
| |
| | +---------------+
| |--(3)-- Authorization Grant -->| Authorization |
| Client | | Server |
| |<-(4)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(5)----- Access Token ------>| Resource |
| | | Server |
| |<-(6)--- Protected Resource ---| |
+--------+ +---------------+
Figure 1: Abstract Protocol Flow
The abstract OAuth 2.1 flow illustrated in Figure 1 describes the
interaction between the four roles and includes the following steps:
1. 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.
2. The client receives an authorization grant, which is a credential
representing the resource owner's authorization, expressed using
one of two 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.
3. The client requests an access token by authenticating with the
authorization server and presenting the authorization grant.
4. The authorization server authenticates the client and validates
the authorization grant, and if valid, issues an access token.
5. The client requests the protected resource from the resource
server and authenticates by presenting the access token.
6. The resource server validates the access token, and if valid,
serves the request.
Hardt, et al. Expires 8 September 2020 [Page 7]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
The preferred method for the client to obtain an authorization grant
from the resource owner (depicted in steps (1) and (2)) 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 two
grant types - authorization code 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. 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.
Hardt, et al. Expires 8 September 2020 [Page 8]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
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 may be extended beyond
what is described in this specification.
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 (4) in
Figure 2).
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.
Hardt, et al. Expires 8 September 2020 [Page 9]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
+--------+ +---------------+
| |--(1)------- Authorization Grant --------->| |
| | | |
| |<-(2)----------- Access Token -------------| |
| | & Refresh Token | |
| | | |
| | +----------+ | |
| |--(3)---- Access Token ---->| | | |
| | | | | |
| |<-(4)- Protected Resource --| Resource | | Authorization |
| Client | | Server | | Server |
| |--(5)---- Access Token ---->| | | |
| | | | | |
| |<-(6)- Invalid Token Error -| | | |
| | +----------+ | |
| | | |
| |--(7)----------- Refresh Token ----------->| |
| | | |
| |<-(8)----------- Access Token -------------| |
+--------+ & Optional Refresh Token +---------------+
Figure 2: Refreshing an Expired Access Token
The flow illustrated in Figure 2 includes the following steps:
1. The client requests an access token by authenticating with the
authorization server and presenting an authorization grant.
2. The authorization server authenticates the client and validates
the authorization grant, and if valid, issues an access token and
a refresh token.
3. The client makes a protected resource request to the resource
server by presenting the access token.
4. The resource server validates the access token, and if valid,
serves the request.
5. Steps (3) and (4) repeat until the access token expires. If the
client knows the access token expired, it skips to step (7);
otherwise, it makes another protected resource request.
6. Since the access token is invalid, the resource server returns an
invalid token error.
7. The client requests a new access token by authenticating with the
authorization server and presenting the refresh token. The
Hardt, et al. Expires 8 September 2020 [Page 10]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
client authentication requirements are based on the client type
and on the authorization server policies.
8. 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 (3), (4), (5), and (6) 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, At the time of this
writing, TLS version 1.3 [RFC8446] is the most recent version.
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 2.1 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.
Hardt, et al. Expires 8 September 2020 [Page 11]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
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.
2. Client Registration
Before initiating the protocol, the client registers with the
authorization server. The means through which the client registers
with the authorization server are beyond the scope of this
specification but typically involve end-user interaction with an HTML
registration form.
Client registration does not require a direct interaction between the
client and the authorization server. When supported by the
authorization server, registration can rely on other means for
establishing trust and obtaining the required client properties
(e.g., redirection URI, client type). For example, registration can
be accomplished using a self-issued or third-party-issued assertion,
or by the authorization server performing client discovery using a
trusted channel.
When registering a client, the client developer SHALL:
* specify the client type as described in Section 2.1,
* provide its client redirection URIs as described in Section 3.1.2,
and
* include any other information required by the authorization server
(e.g., application name, website, description, logo image, the
acceptance of legal terms).
Hardt, et al. Expires 8 September 2020 [Page 12]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
2.1. Client Types
OAuth defines two client types, based on whether they can be issued
credentials that they can use to authenticate at the authorization
server:
"confidential": Clients capable of maintaining the confidentiality
of their credentials (e.g., client implemented on a secure server
with restricted access to the client credentials), or capable of
secure client authentication using other means.
"public": Clients incapable of maintaining the confidentiality of
their credentials (e.g., clients executing on the device used by
the resource owner, such as an installed native application or a
web browser-based application), and incapable of secure client
authentication via any other means.
The client type designation is based on the authorization server's
definition of secure authentication and its acceptable exposure
levels of client credentials. The authorization server SHOULD NOT
make assumptions about the client type.
A client may be implemented as a distributed set of components, each
with a different client type and security context (e.g., a
distributed client with both a confidential server-based component
and a public browser-based component). If the authorization server
does not provide support for such clients or does not provide
guidance with regard to their registration, the client SHOULD
register each component as a separate client.
This specification has been designed around the following client
profiles:
"web application": A web application is a confidential client
running on a web server. Resource owners access the client via an
HTML user interface rendered in a user-agent on the device used by
the resource owner. The client credentials as well as any access
token issued to the client are stored on the web server and are
not exposed to or accessible by the resource owner.
"browser-based application": A browser-based application is a public
client in which the client code is downloaded from a web server
and executes within a user-agent (e.g., web browser) on the device
used by the resource owner. Protocol data and credentials are
easily accessible (and often visible) to the resource owner.
Since such applications reside within the user-agent, they can
make seamless use of the user-agent capabilities when requesting
authorization.
Hardt, et al. Expires 8 September 2020 [Page 13]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
"native application": A native application is a public client
installed and executed on the device used by the resource owner.
Protocol data and credentials are accessible to the resource
owner. It is assumed that any client authentication credentials
included in the application can be extracted. On the other hand,
dynamically issued credentials such as access tokens or refresh
tokens can receive an acceptable level of protection. At a
minimum, these credentials are protected from hostile servers with
which the application may interact. On some platforms, these
credentials might be protected from other applications residing on
the same device.
2.2. Client Identifier
The authorization server issues the registered client a client
identifier - a unique string representing the registration
information provided by the client. The client identifier is not a
secret; it is exposed to the resource owner and MUST NOT be used
alone for client authentication. The client identifier is unique to
the authorization server.
The client identifier string size is left undefined by this
specification. The client should avoid making assumptions about the
identifier size. The authorization server SHOULD document the size
of any identifier it issues.
Authorization servers SHOULD NOT allow clients to influence their
"client_id" or "sub" value or any other claim if that can cause
confusion with a genuine resource owner.
2.3. Client Authentication
If the client type is confidential, the client and authorization
server establish a client authentication method suitable for the
security requirements of the authorization server. The authorization
server MAY accept any form of client authentication meeting its
security requirements.
Confidential clients are typically issued (or establish) a set of
client credentials used for authenticating with the authorization
server (e.g., password, public/private key pair).
Authorization servers SHOULD use client authentication if possible.
It is RECOMMENDED to use asymmetric (public-key based) methods for
client authentication such as mTLS [RFC8705] or "private_key_jwt"
[OpenID]. When asymmetric methods for client authentication are
Hardt, et al. Expires 8 September 2020 [Page 14]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
used, authorization servers do not need to store sensitive symmetric
keys, making these methods more robust against a number of attacks.
The authorization server MAY establish a client authentication method
with public clients. However, the authorization server MUST NOT rely
on public client authentication for the purpose of identifying the
client.
The client MUST NOT use more than one authentication method in each
request.
2.3.1. Client Password
Clients in possession of a client password MAY use the HTTP Basic
authentication scheme as defined in [RFC2617] to authenticate with
the authorization server. The client identifier is encoded using the
"application/x-www-form-urlencoded" encoding algorithm per
Appendix B, and the encoded value is used as the username; the client
password is encoded using the same algorithm and used as the
password. The authorization server MUST support the HTTP Basic
authentication scheme for authenticating clients that were issued a
client password.
For example (with extra line breaks for display purposes only):
Authorization: Basic czZCaGRSa3F0Mzo3RmpmcDBaQnIxS3REUmJuZlZkbUl3
Alternatively, the authorization server MAY support including the
client credentials in the request-body using the following
parameters:
"client_id": REQUIRED. The client identifier issued to the client
during the registration process described by Section 2.2.
"client_secret": REQUIRED. The client secret. The client MAY omit
the parameter if the client secret is an empty string.
Including the client credentials in the request-body using the two
parameters is NOT RECOMMENDED and SHOULD be limited to clients unable
to directly utilize the HTTP Basic authentication scheme (or other
password-based HTTP authentication schemes). The parameters can only
be transmitted in the request-body and MUST NOT be included in the
request URI.
For example, a request to refresh an access token (Section 6) using
the body parameters (with extra line breaks for display purposes
only):
Hardt, et al. Expires 8 September 2020 [Page 15]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
grant_type=refresh_token&refresh_token=tGzv3JOkF0XG5Qx2TlKWIA
&client_id=s6BhdRkqt3&client_secret=7Fjfp0ZBr1KtDRbnfVdmIw
The authorization server MUST require the use of TLS as described in
Section 1.6 when sending requests using password authentication.
Since this client authentication method involves a password, the
authorization server MUST protect any endpoint utilizing it against
brute force attacks.
2.3.2. Other Authorization Methods
The authorization server MAY support any suitable HTTP authentication
scheme matching its security requirements. When using other
authentication methods, the authorization server MUST define a
mapping between the client identifier (registration record) and
authentication scheme.
2.4. Unregistered Clients
This specification does not exclude the use of unregistered clients.
However, the use of such clients is beyond the scope of this
specification and requires additional security analysis and review of
its interoperability impact.
3. Protocol Endpoints
The authorization process utilizes two authorization server endpoints
(HTTP resources):
* Authorization endpoint - used by the client to obtain
authorization from the resource owner via user-agent redirection.
* Token endpoint - used by the client to exchange an authorization
grant for an access token, typically with client authentication.
As well as one client endpoint:
* Redirection endpoint - used by the authorization server to return
responses containing authorization credentials to the client via
the resource owner user-agent.
Not every authorization grant type utilizes both endpoints.
Extension grant types MAY define additional endpoints as needed.
Hardt, et al. Expires 8 September 2020 [Page 16]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
3.1. Authorization Endpoint
The authorization endpoint is used to interact with the resource
owner and obtain an authorization grant. The authorization server
MUST first verify the identity of the resource owner. The way in
which the authorization server authenticates the resource owner
(e.g., username and password login, session cookies) is beyond the
scope of this specification.
The means through which the client obtains the location of the
authorization endpoint are beyond the scope of this specification,
but the location is typically provided in the service documentation.
The endpoint URI MAY include an "application/x-www-form-urlencoded"
formatted (per Appendix B) query component ([RFC3986] Section 3.4),
which MUST be retained when adding additional query parameters. The
endpoint URI MUST NOT include a fragment component.
Since requests to the authorization endpoint result in user
authentication and the transmission of clear-text credentials (in the
HTTP response), the authorization server MUST require the use of TLS
as described in Section 1.6 when sending requests to the
authorization endpoint.
The authorization server MUST support the use of the HTTP "GET"
method [RFC2616] for the authorization endpoint and MAY support the
use of the "POST" method as well.
Parameters sent without a value MUST be treated as if they were
omitted from the request. The authorization server MUST ignore
unrecognized request parameters. Request and response parameters
MUST NOT be included more than once.
3.1.1. Response Type
The authorization endpoint is used by the authorization code flow.
The client informs the authorization server of the desired grant type
using the following parameter:
"response_type": REQUIRED. The value MUST be "code" for requesting
an authorization code as described by Section 4.1.1, or a
registered extension value as described by Section 8.4.
Extension response types MAY contain a space-delimited (%x20) list of
values, where the order of values does not matter (e.g., response
type "a b" is the same as "b a"). The meaning of such composite
response types is defined by their respective specifications.
Hardt, et al. Expires 8 September 2020 [Page 17]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
For example, OpenID Connect defines "response_type=id_token" as well
as a few other combinations which include additional security
features for those flows.
If an authorization request is missing the "response_type" parameter,
or if the response type is not understood, the authorization server
MUST return an error response as described in Section 4.1.2.1.
3.1.2. Redirection Endpoint
After completing its interaction with the resource owner, the
authorization server directs the resource owner's user-agent back to
the client. The authorization server redirects the user-agent to the
client's redirection endpoint previously established with the
authorization server during the client registration process.
The authorization server MUST compare the two URIs using simple
string comparison as defined in [RFC3986], Section 6.2.1.
The redirection endpoint URI MUST be an absolute URI as defined by
[RFC3986] Section 4.3. The endpoint URI MAY include an "application/
x-www-form-urlencoded" formatted (per Appendix B) query component
([RFC3986] Section 3.4), which MUST be retained when adding
additional query parameters. The endpoint URI MUST NOT include a
fragment component.
3.1.2.1. Endpoint Request Confidentiality
The redirection endpoint SHOULD require the use of TLS as described
in Section 1.6 when the requested response type is "code", or when
the redirection request will result in the transmission of sensitive
credentials over an open network. This specification does not
mandate the use of TLS because at the time of this writing, requiring
clients to deploy TLS is a significant hurdle for many client
developers. If TLS is not available, the authorization server SHOULD
warn the resource owner about the insecure endpoint prior to
redirection (e.g., display a message during the authorization
request).
Lack of transport-layer security can have a severe impact on the
security of the client and the protected resources it is authorized
to access. The use of transport-layer security is particularly
critical when the authorization process is used as a form of
delegated end-user authentication by the client (e.g., third-party
sign-in service).
Hardt, et al. Expires 8 September 2020 [Page 18]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
3.1.2.2. Registration Requirements
The authorization server MUST require all clients to register their
redirection endpoint prior to utilizing the authorization endpoint.
The authorization server SHOULD require the client to provide the
complete redirection URI (the client MAY use the "state" request
parameter to achieve per-request customization).
The authorization server MAY allow the client to register multiple
redirection endpoints.
Lack of a redirection URI registration requirement can enable an
attacker to use the authorization endpoint as an open redirector as
described in Section 9.17.
3.1.2.3. Dynamic Configuration
If multiple redirection URIs have been registered the client MUST
include a redirection URI with the authorization request using the
"redirect_uri" request parameter.
When a redirection URI is included in an authorization request, the
authorization server MUST compare and match the value received
against at least one of the registered redirection URIs (or URI
components) as defined in [RFC3986] Section 6, if any redirection
URIs were registered. If the client registration included the full
redirection URI, the authorization server MUST compare the two URIs
using simple string comparison as defined in [RFC3986] Section 6.2.1.
3.1.2.4. Invalid Endpoint
If an authorization request fails validation due to a missing,
invalid, or mismatching redirection URI, the authorization server
SHOULD inform the resource owner of the error and MUST NOT
automatically redirect the user-agent to the invalid redirection URI.
3.1.2.5. Endpoint Content
The redirection request to the client's endpoint typically results in
an HTML document response, processed by the user-agent. If the HTML
response is served directly as the result of the redirection request,
any script included in the HTML document will execute with full
access to the redirection URI and the credentials it contains.
The client SHOULD NOT include any third-party scripts (e.g., third-
party analytics, social plug-ins, ad networks) in the redirection
endpoint response. Instead, it SHOULD extract the credentials from
Hardt, et al. Expires 8 September 2020 [Page 19]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
the URI and redirect the user-agent again to another endpoint without
exposing the credentials (in the URI or elsewhere). If third-party
scripts are included, the client MUST ensure that its own scripts
(used to extract and remove the credentials from the URI) will
execute first.
3.2. Token Endpoint
The token endpoint is used by the client to obtain an access token by
presenting its authorization grant or refresh token.
The means through which the client obtains the location of the token
endpoint are beyond the scope of this specification, but the location
is typically provided in the service documentation.
The endpoint URI MAY include an "application/x-www-form-urlencoded"
formatted (per Appendix B) query component ([RFC3986] Section 3.4),
which MUST be retained when adding additional query parameters. The
endpoint URI MUST NOT include a fragment component.
Since requests to the token endpoint result in the transmission of
clear-text credentials (in the HTTP request and response), the
authorization server MUST require the use of TLS as described in
Section 1.6 when sending requests to the token endpoint.
The client MUST use the HTTP "POST" method when making access token
requests.
Parameters sent without a value MUST be treated as if they were
omitted from the request. The authorization server MUST ignore
unrecognized request parameters. Request and response parameters
MUST NOT be included more than once.
3.2.1. Client Authentication
Confidential clients or other clients issued client credentials MUST
authenticate with the authorization server as described in
Section 2.3 when making requests to the token endpoint. Client
authentication is used for:
* Enforcing the binding of refresh tokens and authorization codes to
the client they were issued to. Client authentication is critical
when an authorization code is transmitted to the redirection
endpoint over an insecure channel or when the redirection URI has
not been registered in full.
* Recovering from a compromised client by disabling the client or
changing its credentials, thus preventing an attacker from abusing
Hardt, et al. Expires 8 September 2020 [Page 20]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
stolen refresh tokens. Changing a single set of client
credentials is significantly faster than revoking an entire set of
refresh tokens.
* Implementing authentication management best practices, which
require periodic credential rotation. Rotation of an entire set
of refresh tokens can be challenging, while rotation of a single
set of client credentials is significantly easier.
A client MAY use the "client_id" request parameter to identify itself
when sending requests to the token endpoint. In the
"authorization_code" "grant_type" request to the token endpoint, an
unauthenticated client MUST send its "client_id" to prevent itself
from inadvertently accepting a code intended for a client with a
different "client_id". This protects the client from substitution of
the authentication code. (It provides no additional security for the
protected resource.)
3.3. Access Token Scope
The authorization and token endpoints allow the client to specify the
scope of the access request using the "scope" request parameter. In
turn, the authorization server uses the "scope" response parameter to
inform the client of the scope of the access token issued.
The value of the scope parameter is expressed as a list of space-
delimited, case-sensitive strings. The strings are defined by the
authorization server. If the value contains multiple space-delimited
strings, their order does not matter, and each string adds an
additional access range to the requested scope.
scope = scope-token *( SP scope-token )
scope-token = 1*( %x21 / %x23-5B / %x5D-7E )
The authorization server MAY fully or partially ignore the scope
requested by the client, based on the authorization server policy or
the resource owner's instructions. If the issued access token scope
is different from the one requested by the client, the authorization
server MUST include the "scope" response parameter to inform the
client of the actual scope granted.
If the client omits the scope parameter when requesting
authorization, the authorization server MUST either process the
request using a pre-defined default value or fail the request
indicating an invalid scope. The authorization server SHOULD
document its scope requirements and default value (if defined).
Hardt, et al. Expires 8 September 2020 [Page 21]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
4. Obtaining Authorization
To request an access token, the client obtains authorization from the
resource owner. The authorization is expressed in the form of an
authorization grant, which the client uses to request the access
token. OAuth defines two grant types: authorization code and client
credentials. It also provides an extension mechanism for defining
additional grant types.
4.1. Authorization Code Grant
The authorization code grant type is used to obtain both access
tokens and refresh tokens.
Since this is a redirection-based flow, the client must be capable of
interacting with the resource owner's user-agent (typically a web
browser) and capable of receiving incoming requests (via redirection)
from the authorization server.
+----------+
| Resource |
| Owner |
| |
+----------+
^
|
(2)
+----|-----+ Client Identifier +---------------+
| -+----(1)-- & Redirection URI ---->| |
| User- | | Authorization |
| Agent -+----(2)-- User authenticates --->| Server |
| | | |
| -+----(3)-- Authorization Code ---<| |
+-|----|---+ +---------------+
| | ^ v
(1) (3) | |
| | | |
^ v | |
+---------+ | |
| |>---(4)-- Authorization Code ---------' |
| Client | & Redirection URI |
| | |
| |<---(5)----- Access Token -------------------'
+---------+ (w/ Optional Refresh Token)
Note: The lines illustrating steps (1), (2), and (3) are broken into
two parts as they pass through the user-agent.
Hardt, et al. Expires 8 September 2020 [Page 22]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
Figure 3: Authorization Code Flow
The flow illustrated in Figure 3 includes the following steps:
(1) The client initiates the flow by directing the resource owner's
user-agent to the authorization endpoint. The client includes its
client identifier, requested scope, local state, PKCE code challenge,
and a redirection URI to which the authorization server will send the
user-agent back once access is granted (or denied).
(2) The authorization server authenticates the resource owner (via
the user-agent) and establishes whether the resource owner grants or
denies the client's access request.
(3) Assuming the resource owner grants access, the authorization
server redirects the user-agent back to the client using the
redirection URI provided earlier (in the request or during client
registration). The redirection URI includes an authorization code
and any local state provided by the client earlier.
(4) The client requests an access token from the authorization
server's token endpoint by including the authorization code received
in the previous step, and including its code verifier. When making
the request, the client authenticates with the authorization server
if it can. The client includes the redirection URI used to obtain
the authorization code for verification.
(5) The authorization server authenticates the client when possible,
validates the authorization code, validates the code verifier, and
ensures that the redirection URI received matches the URI used to
redirect the client in step (C). If valid, the authorization server
responds back with an access token and, optionally, a refresh token.
4.1.1. Authorization Request
To begin the authorization request, the client builds the
authorization request URI by adding parameters to the authorization
server's authorization endpoint URI.
Without a client secret, public clients would be susceptible to an
authorization code interception attack, where an attacker is able to
intercept the authorization response through various means and use
the authorization code to obtain an access token. To protect against
this attack, as well as to protect against CSRF attacks, the client
first generates a unique secret per authorization request, which it
can later use along with the authorization code to prove that the
application using the authorization code is the same application that
requested it. This practice is known as "Proof-Key for Code
Hardt, et al. Expires 8 September 2020 [Page 23]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
Exchange", or PKCE, after the OAuth 2.0 extension ([RFC7636]) where
it was originally developed.
4.1.1.1. Client Creates a PKCE Code Verifier
The client first creates a PKCE code verifier, "code_verifier", for
each Authorization Request, in the following manner:
code_verifier = high-entropy cryptographic random STRING using the
unreserved characters `[A-Z] / [a-z] / [0-9] / "-" / "." / "_" / "~"`
from Section 2.3 of {{RFC3986}}, with a minimum length of 43 characters
and a maximum length of 128 characters.
ABNF for "code_verifier" is as follows.
code-verifier = 43*128unreserved
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
ALPHA = %x41-5A / %x61-7A
DIGIT = %x30-39
NOTE: The code verifier SHOULD have enough entropy to make it
impractical to guess the value. It is RECOMMENDED that the output of
a suitable random number generator be used to create a 32-octet
sequence. The octet sequence is then base64url-encoded to produce a
43-octet URL-safe string to use as the code verifier.
4.1.1.2. Client Creates the PKCE Code Challenge
The client then creates a PKCE code challenge derived from the code
verifier by using one of the following transformations on the code
verifier:
plain
code_challenge = code_verifier
S256
code_challenge = BASE64URL-ENCODE(SHA256(ASCII(code_verifier)))
If the client is capable of using "S256", it MUST use "S256", as
"S256" is Mandatory To Implement (MTI) on the server. Clients are
permitted to use "plain" only if they cannot support "S256" for some
technical reason and know via out-of-band configuration that the
server supports "plain".
The plain transformation is for compatibility with existing
deployments and for constrained environments that can't use the S256
transformation.
Hardt, et al. Expires 8 September 2020 [Page 24]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
ABNF for "code_challenge" is as follows.
code-challenge = 43*128unreserved
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
ALPHA = %x41-5A / %x61-7A
DIGIT = %x30-39
4.1.1.3. Client Initiates the Authorization Request
The client constructs the request URI by adding the following
parameters to the query component of the authorization endpoint URI
using the "application/x-www-form-urlencoded" format, per Appendix B:
"response_type": REQUIRED. Value MUST be set to "code".
"client_id": REQUIRED. The client identifier as described in
Section 2.2.
"code_challenge": REQUIRED. Code challenge.
"code_challenge_method": OPTIONAL, defaults to "plain" if not
present in the request. Code nverifier transformation method is
"S256" or "plain".
"redirect_uri": OPTIONAL. As described in Section 3.1.2.
"scope": OPTIONAL. The scope of the access request as described by
Section 3.3.
"state": OPTIONAL. An opaque value used by the client to maintain
state between the request and callback. The authorization server
includes this value when redirecting the user-agent back to the
client.
The client directs the resource owner to the constructed URI using an
HTTP redirection response, or by other means available to it via the
user-agent.
For example, the client directs the user-agent to make the following
HTTP request using TLS (with extra line breaks for display purposes
only):
GET /authorize?response_type=code&client_id=s6BhdRkqt3&state=xyz
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
&code_challenge=6fdkQaPm51l13DSukcAH3Mdx7_ntecHYd1vi3n0hMZY
&code_challenge_method=S256 HTTP/1.1
Host: server.example.com
Hardt, et al. Expires 8 September 2020 [Page 25]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
The authorization server validates the request to ensure that all
required parameters are present and valid. If the request is valid,
the authorization server authenticates the resource owner and obtains
an authorization decision (by asking the resource owner or by
establishing approval via other means).
When a decision is established, the authorization server directs the
user-agent to the provided client redirection URI using an HTTP
redirection response, or by other means available to it via the user-
agent.
4.1.2. Authorization Response
If the resource owner grants the access request, the authorization
server issues an authorization code and delivers it to the client by
adding the following parameters to the query component of the
redirection URI using the "application/x-www-form-urlencoded" format,
per Appendix B:
"code": REQUIRED. The authorization code generated by the
authorization server. The authorization code MUST expire shortly
after it is issued to mitigate the risk of leaks. A maximum
authorization code lifetime of 10 minutes is RECOMMENDED. The
client MUST NOT use the authorization code more than once. If an
authorization code is used more than once, the authorization
server MUST deny the request and SHOULD revoke (when possible) all
tokens previously issued based on that authorization code. The
authorization code is bound to the client identifier and
redirection URI.
"state": REQUIRED if the "state" parameter was present in the client
authorization request. The exact value received from the client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb?code=SplxlOBeZQQYbYS6WxSbIA
&state=xyz
The client MUST ignore unrecognized response parameters. The
authorization code string size is left undefined by this
specification. The client should avoid making assumptions about code
value sizes. The authorization server SHOULD document the size of
any value it issues.
When the server issues the authorization code in the authorization
response, it MUST associate the "code_challenge" and
Hardt, et al. Expires 8 September 2020 [Page 26]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
"code_challenge_method" values with the authorization code so it can
be verified later.
Typically, the "code_challenge" and "code_challenge_method" values
are stored in encrypted form in the "code" itself but could
alternatively be stored on the server associated with the code. The
server MUST NOT include the "code_challenge" value in client requests
in a form that other entities can extract.
The exact method that the server uses to associate the
"code_challenge" with the issued "code" is out of scope for this
specification.
4.1.2.1. Error Response
If the request fails due to a missing, invalid, or mismatching
redirection URI, or if the client identifier is missing or invalid,
the authorization server SHOULD inform the resource owner of the
error and MUST NOT automatically redirect the user-agent to the
invalid redirection URI.
If the client does not send the "code_challenge" in the request, the
authorization endpoint MUST return the authorization error response
with the "error" value set to "invalid_request". The
"error_description" or the response of "error_uri" SHOULD explain the
nature of error, e.g., code challenge required.
If the server supporting PKCE does not support the requested
transformation, the authorization endpoint MUST return the
authorization error response with "error" value set to
"invalid_request". The "error_description" or the response of
"error_uri" SHOULD explain the nature of error, e.g., transform
algorithm not supported.
If the resource owner denies the access request or if the request
fails for reasons other than a missing or invalid redirection URI,
the authorization server informs the client by adding the following
parameters to the query component of the redirection URI using the
"application/x-www-form-urlencoded" format, per Appendix B:
"error": REQUIRED. A single ASCII [USASCII] error code from the
following:
"invalid_request": The request is missing a required parameter,
includes an invalid parameter value, includes a parameter more
than once, or is otherwise malformed.
"unauthorized_client": The client is not authorized to request an
Hardt, et al. Expires 8 September 2020 [Page 27]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
authorization code using this method.
"access_denied": The resource owner or authorization server
denied the request.
"unsupported_response_type": The authorization server does not
support obtaining an authorization code using this method.
"invalid_scope": The requested scope is invalid, unknown, or
malformed.
"server_error": The authorization server encountered an
unexpected condition that prevented it from fulfilling the
request. (This error code is needed because a 500 Internal
Server Error HTTP status code cannot be returned to the client
via an HTTP redirect.)
"temporarily_unavailable": The authorization server is currently
unable to handle the request due to a temporary overloading or
maintenance of the server. (This error code is needed because
a 503 Service Unavailable HTTP status code cannot be returned
to the client via an HTTP redirect.)
Values for the "error" parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_description": OPTIONAL. Human-readable ASCII [USASCII] text
providing additional information, used to assist the client
developer in understanding the error that occurred. Values for
the "error_description" parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_uri": OPTIONAL. A URI identifying a human-readable web page
with information about the error, used to provide the client
developer with additional information about the error. Values for
the "error_uri" parameter MUST conform to the URI-reference syntax
and thus MUST NOT include characters outside the set %x21 /
%x23-5B / %x5D-7E.
"state": REQUIRED if a "state" parameter was present in the client
authorization request. The exact value received from the client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb?error=access_denied&state=xyz
Hardt, et al. Expires 8 September 2020 [Page 28]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
4.1.3. Access Token Request
The client makes a request to the token endpoint by sending the
following parameters using the "application/x-www-form-urlencoded"
format per Appendix B with a character encoding of UTF-8 in the HTTP
request entity-body:
"grant_type": REQUIRED. Value MUST be set to "authorization_code".
"code": REQUIRED. The authorization code received from the
authorization server.
"redirect_uri": REQUIRED, if the "redirect_uri" parameter was
included in the authorization request as described in
Section 4.1.1, and their values MUST be identical.
"client_id": REQUIRED, if the client is not authenticating with the
authorization server as described in Section 3.2.1.
"code_verifier": REQUIRED. Code verifier
If the client type is confidential or the client was issued client
credentials (or assigned other authentication requirements), the
client MUST authenticate with the authorization server as described
in Section 3.2.1.
For example, the client makes the following HTTP request using TLS
(with extra line breaks for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=authorization_code&code=SplxlOBeZQQYbYS6WxSbIA
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
&code_verifier=3641a2d12d66101249cdf7a79c000c1f8c05d2aafcf14bf146497bed
The authorization server MUST:
* require client authentication for confidential clients or for any
client that was issued client credentials (or with other
authentication requirements),
* authenticate the client if client authentication is included,
* ensure that the authorization code was issued to the authenticated
Hardt, et al. Expires 8 September 2020 [Page 29]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
confidential client, or if the client is public, ensure that the
code was issued to "client_id" in the request,
* verify that the authorization code is valid,
* verify the "code_verifier" by calculating the code challenge from
the received "code_verifier" and comparing it with the previously
associated "code_challenge", after first transforming it according
to the "code_challenge_method" method specified by the client, and
* ensure that the "redirect_uri" parameter is present if the
"redirect_uri" parameter was included in the initial authorization
request as described in Section 4.1.1, and if included ensure that
their values are identical.
4.1.4. Access Token Response
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in Section 5.1. If the request client
authentication failed or is invalid, the authorization server returns
an error response as described in Section 5.2.
An example successful response:
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"access_token": "2YotnFZFEjr1zCsicMWpAA",
"token_type": "Bearer",
"expires_in": 3600,
"refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
"example_parameter": "example_value"
}
4.2. Client Credentials Grant
The client can request an access token using only its client
credentials (or other supported means of authentication) when the
client is requesting access to the protected resources under its
control, or those of another resource owner that have been previously
arranged with the authorization server (the method of which is beyond
the scope of this specification).
Hardt, et al. Expires 8 September 2020 [Page 30]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
The client credentials grant type MUST only be used by confidential
clients.
+---------+ +---------------+
| | | |
| |>--(A)- Client Authentication --->| Authorization |
| Client | | Server |
| |<--(B)---- Access Token ---------<| |
| | | |
+---------+ +---------------+
Figure 4: Client Credentials Flow
The flow illustrated in Figure 4 includes the following steps:
(A) The client authenticates with the authorization server and
requests an access token from the token endpoint.
(B) The authorization server authenticates the client, and if valid,
issues an access token.
4.2.1. Authorization Request and Response
Since the client authentication is used as the authorization grant,
no additional authorization request is needed.
4.2.2. Access Token Request
The client makes a request to the token endpoint by adding the
following parameters using the "application/x-www-form-urlencoded"
format per Appendix B with a character encoding of UTF-8 in the HTTP
request entity-body:
"grant_type": REQUIRED. Value MUST be set to "client_credentials".
"scope": OPTIONAL. The scope of the access request as described by
Section 3.3.
The client MUST authenticate with the authorization server as
described in Section 3.2.1.
For example, the client makes the following HTTP request using
transport-layer security (with extra line breaks for display purposes
only):
Hardt, et al. Expires 8 September 2020 [Page 31]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=client_credentials
The authorization server MUST authenticate the client.
4.2.3. Access Token Response
If the access token request is valid and authorized, the
authorization server issues an access token as described in
Section 5.1. A refresh token SHOULD NOT be included. If the request
failed client authentication or is invalid, the authorization server
returns an error response as described in Section 5.2.
An example successful response:
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"access_token": "2YotnFZFEjr1zCsicMWpAA",
"token_type": "Bearer",
"expires_in": 3600,
"example_parameter": "example_value"
}
4.3. Extension Grants
The client uses an extension grant type by specifying the grant type
using an absolute URI (defined by the authorization server) as the
value of the "grant_type" parameter of the token endpoint, and by
adding any additional parameters necessary.
For example, to request an access token using a Security Assertion
Markup Language (SAML) 2.0 assertion grant type as defined by
[RFC7522], the client could make the following HTTP request using TLS
(with extra line breaks for display purposes only):
Hardt, et al. Expires 8 September 2020 [Page 32]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Asaml2-
bearer&assertion=PEFzc2VydGlvbiBJc3N1ZUluc3RhbnQ9IjIwMTEtMDU
[...omitted for brevity...]aG5TdGF0ZW1lbnQ-PC9Bc3NlcnRpb24-
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in Section 5.1. If the request failed client
authentication or is invalid, the authorization server returns an
error response as described in Section 5.2.
5. Issuing an Access Token
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in Section 5.1. If the request failed client
authentication or is invalid, the authorization server returns an
error response as described in Section 5.2.
5.1. Successful Response
The authorization server issues an access token and optional refresh
token, and constructs the response by adding the following parameters
to the entity-body of the HTTP response with a 200 (OK) status code:
"access_token": REQUIRED. The access token issued by the
authorization server.
"token_type": REQUIRED. The type of the token issued as described
in Section 7.1. Value is case insensitive.
"expires_in": RECOMMENDED. The lifetime in seconds of the access
token. For example, the value "3600" denotes that the access
token will expire in one hour from the time the response was
generated. If omitted, the authorization server SHOULD provide
the expiration time via other means or document the default value.
"refresh_token": OPTIONAL. The refresh token, which can be used to
obtain new access tokens using the same authorization grant as
described in Section 6.
"scope": OPTIONAL, if identical to the scope requested by the
client; otherwise, REQUIRED. The scope of the access token as
described by Section 3.3.
Hardt, et al. Expires 8 September 2020 [Page 33]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
The parameters are included in the entity-body of the HTTP response
using the "application/json" media type as defined by [RFC4627]. The
parameters are serialized into a JavaScript Object Notation (JSON)
structure by adding each parameter at the highest structure level.
Parameter names and string values are included as JSON strings.
Numerical values are included as JSON numbers. The order of
parameters does not matter and can vary.
The authorization server MUST include the HTTP "Cache-Control"
response header field [RFC2616] with a value of "no-store" in any
response containing tokens, credentials, or other sensitive
information, as well as the "Pragma" response header field [RFC2616]
with a value of "no-cache".
For example:
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"access_token":"2YotnFZFEjr1zCsicMWpAA",
"token_type":"Bearer",
"expires_in":3600,
"refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA",
"example_parameter":"example_value"
}
The client MUST ignore unrecognized value names in the response. The
sizes of tokens and other values received from the authorization
server are left undefined. The client should avoid making
assumptions about value sizes. The authorization server SHOULD
document the size of any value it issues.
5.2. Error Response
The authorization server responds with an HTTP 400 (Bad Request)
status code (unless specified otherwise) and includes the following
parameters with the response:
The authorization server responds with an HTTP 400 (Bad Request)
status code (unless specified otherwise) and includes the following
parameters with the response:
"error": REQUIRED. A single ASCII [USASCII] error code from the
following:
Hardt, et al. Expires 8 September 2020 [Page 34]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
"invalid_request": The request is missing a required parameter,
includes an unsupported parameter value (other than grant
type), repeats a parameter, includes multiple credentials,
utilizes more than one mechanism for authenticating the client,
or is otherwise malformed.
"invalid_client": Client authentication failed (e.g., unknown
client, no client authentication included, or unsupported
authentication method). The authorization server MAY return an
HTTP 401 (Unauthorized) status code to indicate which HTTP
authentication schemes are supported. If the client attempted
to authenticate via the "Authorization" request header field,
the authorization server MUST respond with an HTTP 401
(Unauthorized) status code and include the "WWW-Authenticate"
response header field matching the authentication scheme used
by the client.
"invalid_grant": The provided authorization grant (e.g.,
authorization code, resource owner credentials) or refresh
token is invalid, expired, revoked, does not match the
redirection URI used in the authorization request, or was
issued to another client.
"unauthorized_client": The authenticated client is not authorized
to use this authorization grant type.
"unsupported_grant_type": The authorization grant type is not
supported by the authorization server.
"invalid_scope": The requested scope is invalid, unknown,
malformed, or exceeds the scope granted by the resource owner.
Values for the "error" parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_description": OPTIONAL. Human-readable ASCII [USASCII] text
providing additional information, used to assist the client
developer in understanding the error that occurred. Values for
the "error_description" parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_uri": OPTIONAL. A URI identifying a human-readable web page
with information about the error, used to provide the client
developer with additional information about the error. Values for
the "error_uri" parameter MUST conform to the URI-reference syntax
and thus MUST NOT include characters outside the set %x21 /
%x23-5B / %x5D-7E.
Hardt, et al. Expires 8 September 2020 [Page 35]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
The parameters are included in the entity-body of the HTTP response
using the "application/json" media type as defined by [RFC4627]. The
parameters are serialized into a JSON structure by adding each
parameter at the highest structure level. Parameter names and string
values are included as JSON strings. Numerical values are included
as JSON numbers. The order of parameters does not matter and can
vary.
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"error":"invalid_request"
}
6. Refreshing an Access Token
Authorization servers SHOULD determine, based on a risk assessment,
whether to issue refresh tokens to a certain client. If the
authorization server decides not to issue refresh tokens, the client
MAY refresh access tokens by utilizing other grant types, such as the
authorization code grant type. In such a case, the authorization
server may utilize cookies and persistent grants to optimize the user
experience.
If refresh tokens are issued, those refresh tokens MUST be bound to
the scope and resource servers as consented by the resource owner.
This is to prevent privilege escalation by the legitimate client and
reduce the impact of refresh token leakage.
If the authorization server issued a refresh token to the client, the
client makes a refresh request to the token endpoint by adding the
following parameters using the "application/x-www-form-urlencoded"
format per Appendix B with a character encoding of UTF-8 in the HTTP
request entity-body:
"grant_type": REQUIRED. Value MUST be set to "refresh_token".
"refresh_token": REQUIRED. The refresh token issued to the client.
"scope": OPTIONAL. The scope of the access request as described by
Section 3.3. The requested scope MUST NOT include any scope not
originally granted by the resource owner, and if omitted is
Hardt, et al. Expires 8 September 2020 [Page 36]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
treated as equal to the scope originally granted by the resource
owner.
Because refresh tokens are typically long-lasting credentials used to
request additional access tokens, the refresh token is bound to the
client to which it was issued. If the client type is confidential or
the client was issued client credentials (or assigned other
authentication requirements), the client MUST authenticate with the
authorization server as described in Section 3.2.1.
For example, the client makes the following HTTP request using
transport-layer security (with extra line breaks for display purposes
only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=refresh_token&refresh_token=tGzv3JOkF0XG5Qx2TlKWIA
The authorization server MUST:
* require client authentication for confidential clients or for any
client that was issued client credentials (or with other
authentication requirements),
* authenticate the client if client authentication is included and
ensure that the refresh token was issued to the authenticated
client, and
* validate the refresh token.
Authorization server MUST utilize one of these methods to detect
refresh token replay by malicious actors for public clients:
* _Sender-constrained refresh tokens:_ the authorization server
cryptographically binds the refresh token to a certain client
instance by utilizing [I-D.ietf-oauth-token-binding] or [RFC8705].
* _Refresh token rotation:_ the authorization server issues a new
refresh token with every access token refresh response. The
previous refresh token is invalidated but information about the
relationship is retained by the authorization server. If a
refresh token is compromised and subsequently used by both the
attacker and the legitimate client, one of them will present an
invalidated refresh token, which will inform the authorization
server of the breach. The authorization server cannot determine
Hardt, et al. Expires 8 September 2020 [Page 37]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
which party submitted the invalid refresh token, but it will
revoke the active refresh token. This stops the attack at the
cost of forcing the legitimate client to obtain a fresh
authorization grant.
Implementation note: the grant to which a refresh token belongs
may be encoded into the refresh token itself. This can enable an
authorization server to efficiently determine the grant to which a
refresh token belongs, and by extension, all refresh tokens that
need to be revoked. Authorization servers MUST ensure the
integrity of the refresh token value in this case, for example,
using signatures.
If valid and authorized, the authorization server issues an access
token as described in Section 5.1. If the request failed
verification or is invalid, the authorization server returns an error
response as described in Section 5.2.
The authorization server MAY issue a new refresh token, in which case
the client MUST discard the old refresh token and replace it with the
new refresh token. The authorization server MAY revoke the old
refresh token after issuing a new refresh token to the client. If a
new refresh token is issued, the refresh token scope MUST be
identical to that of the refresh token included by the client in the
request.
Authorization servers MAY revoke refresh tokens automatically in case
of a security event, such as:
* password change
* logout at the authorization server
Refresh tokens SHOULD expire if the client has been inactive for some
time, i.e., the refresh token has not been used to obtain fresh
access tokens for some time. The expiration time is at the
discretion of the authorization server. It might be a global value
or determined based on the client policy or the grant associated with
the refresh token (and its sensitivity).
7. Accessing Protected Resources
The client accesses protected resources by presenting the access
token to the resource server. The resource server MUST validate the
access token and ensure that it has not expired and that its scope
covers the requested resource. The methods used by the resource
server to validate the access token (as well as any error responses)
are beyond the scope of this specification but generally involve an
Hardt, et al. Expires 8 September 2020 [Page 38]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
interaction or coordination between the resource server and the
authorization server.
The method in which the client utilizes the access token to
authenticate with the resource server depends on the type of access
token issued by the authorization server. Typically, it involves
using the HTTP "Authorization" request header field [RFC2617] with an
authentication scheme defined by the specification of the access
token type used, such as "Bearer", defined below.
7.1. Access Token Types
The access token type provides the client with the information
required to successfully utilize the access token to make a protected
resource request (along with type-specific attributes). The client
MUST NOT use an access token if it does not understand the token
type.
For example, the "Bearer" token type defined in this specification is
utilized by simply including the access token string in the request:
GET /resource/1 HTTP/1.1
Host: example.com
Authorization: Bearer mF_9.B5f-4.1JqM
The above example is provided for illustration purposes only.
Each access token type definition specifies the additional attributes
(if any) sent to the client together with the "access_token" response
parameter. It also defines the HTTP authentication method used to
include the access token when making a protected resource request.
7.2. Bearer Tokens
A Bearer Token is a security token with the property that any party
in possession of the token (a "bearer") can use the token in any way
that any other party in possession of it can. Using a bearer token
does not require a bearer to prove possession of cryptographic key
material (proof-of-possession).
Bearer tokens may be extended to include proof-of-possession
techniques by other specifications.
7.2.1. Authenticated Requests
This section defines two methods of sending Bearer tokens in resource
requetss to resource servers. Clients MUST NOT use more than one
method to transmit the token in each request.
Hardt, et al. Expires 8 September 2020 [Page 39]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
7.2.1.1. Authorization Request Header Field
When sending the access token in the "Authorization" request header
field defined by HTTP/1.1 [RFC2617], the client uses the "Bearer"
authentication scheme to transmit the access token.
For example:
GET /resource HTTP/1.1
Host: server.example.com
Authorization: Bearer mF_9.B5f-4.1JqM
The syntax of the "Authorization" header field for this scheme
follows the usage of the Basic scheme defined in Section 2 of
[RFC2617]. Note that, as with Basic, it does not conform to the
generic syntax defined in Section 1.2 of [RFC2617] but is compatible
with the general authentication framework in HTTP 1.1 Authentication
[RFC7235], although it does not follow the preferred practice
outlined therein in order to reflect existing deployments. The
syntax for Bearer credentials is as follows:
b64token = 1*( ALPHA / DIGIT /
"-" / "." / "_" / "~" / "+" / "/" ) *"="
credentials = "Bearer" 1*SP b64token
Clients SHOULD make authenticated requests with a bearer token using
the "Authorization" request header field with the "Bearer" HTTP
authorization scheme. Resource servers MUST support this method.
7.2.1.2. Form-Encoded Body Parameter
When sending the access token in the HTTP request entity-body, the
client adds the access token to the request-body using the
"access_token" parameter. The client MUST NOT use this method unless
all of the following conditions are met:
* The HTTP request entity-header includes the "Content-Type" header
field set to "application/x-www-form-urlencoded".
* The entity-body follows the encoding requirements of the
"application/x-www-form-urlencoded" content-type as defined by
HTML 4.01 [W3C.REC-html401-19991224].
* The HTTP request entity-body is single-part.
* The content to be encoded in the entity-body MUST consist entirely
of ASCII [USASCII] characters.
Hardt, et al. Expires 8 September 2020 [Page 40]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
* The HTTP request method is one for which the request-body has
defined semantics. In particular, this means that the "GET"
method MUST NOT be used.
The entity-body MAY include other request-specific parameters, in
which case the "access_token" parameter MUST be properly separated
from the request-specific parameters using "&" character(s) (ASCII
code 38).
For example, the client makes the following HTTP request using
transport-layer security:
POST /resource HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
access_token=mF_9.B5f-4.1JqM
The "application/x-www-form-urlencoded" method SHOULD NOT be used
except in application contexts where participating clients do not
have access to the "Authorization" request header field. Resource
servers MAY support this method.
7.2.2. The WWW-Authenticate Response Header Field
If the protected resource request does not include authentication
credentials or does not contain an access token that enables access
to the protected resource, the resource server MUST include the HTTP
"WWW-Authenticate" response header field; it MAY include it in
response to other conditions as well. The "WWW-Authenticate" header
field uses the framework defined by HTTP/1.1 [RFC2617].
All challenges defined by this specification MUST use the auth-scheme
value "Bearer". This scheme MUST be followed by one or more auth-
param values. The auth-param attributes used or defined by this
specification are as follows. Other auth-param attributes MAY be
used as well.
A "realm" attribute MAY be included to indicate the scope of
protection in the manner described in HTTP/1.1 [RFC2617]. The
"realm" attribute MUST NOT appear more than once.
The "scope" attribute is defined in Section 3.3. The "scope"
attribute is a space-delimited list of case-sensitive scope values
indicating the required scope of the access token for accessing the
requested resource. "scope" values are implementation defined; there
is no centralized registry for them; allowed values are defined by
the authorization server. The order of "scope" values is not
Hardt, et al. Expires 8 September 2020 [Page 41]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
significant. In some cases, the "scope" value will be used when
requesting a new access token with sufficient scope of access to
utilize the protected resource. Use of the "scope" attribute is
OPTIONAL. The "scope" attribute MUST NOT appear more than once. The
"scope" value is intended for programmatic use and is not meant to be
displayed to end-users.
Two example scope values follow; these are taken from the OpenID
Connect [OpenID.Messages] and the Open Authentication Technology
Committee (OATC) Online Multimedia Authorization Protocol [OMAP]
OAuth 2.0 use cases, respectively:
scope="openid profile email"
scope="urn:example:channel=HBO&urn:example:rating=G,PG-13"
If the protected resource request included an access token and failed
authentication, the resource server SHOULD include the "error"
attribute to provide the client with the reason why the access
request was declined. The parameter value is described in
Section 7.3.1. In addition, the resource server MAY include the
"error_description" attribute to provide developers a human-readable
explanation that is not meant to be displayed to end-users. It also
MAY include the "error_uri" attribute with an absolute URI
identifying a human-readable web page explaining the error. The
"error", "error_description", and "error_uri" attributes MUST NOT
appear more than once.
Values for the "scope" attribute (specified in Appendix A.4) MUST NOT
include characters outside the set %x21 / %x23-5B / %x5D-7E for
representing scope values and %x20 for delimiters between scope
values. Values for the "error" and "error_description" attributes
(specified in Appendixes A.7 and A.8) MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E. Values for the
"error_uri" attribute (specified in Appendix A.9 of) MUST conform to
the URI-reference syntax and thus MUST NOT include characters outside
the set %x21 / %x23-5B / %x5D-7E.
For example, in response to a protected resource request without
authentication:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer realm="example"
And in response to a protected resource request with an
authentication attempt using an expired access token:
Hardt, et al. Expires 8 September 2020 [Page 42]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer realm="example",
error="invalid_token",
error_description="The access token expired"
7.3. Error Response
If a resource access request fails, the resource server SHOULD inform
the client of the error. While the specifics of such error responses
are beyond the scope of this specification, this document establishes
a common registry in Section 12.4 for error values to be shared among
OAuth token authentication schemes.
New authentication schemes designed primarily for OAuth token
authentication SHOULD define a mechanism for providing an error
status code to the client, in which the error values allowed are
registered in the error registry established by this specification.
Such schemes MAY limit the set of valid error codes to a subset of
the registered values. If the error code is returned using a named
parameter, the parameter name SHOULD be "error".
Other schemes capable of being used for OAuth token authentication,
but not primarily designed for that purpose, MAY bind their error
values to the registry in the same manner.
New authentication schemes MAY choose to also specify the use of the
"error_description" and "error_uri" parameters to return error
information in a manner parallel to their usage in this
specification.
7.3.1. Error Codes
When a request fails, the resource server responds using the
appropriate HTTP status code (typically, 400, 401, 403, or 405) and
includes one of the following error codes in the response:
"invalid_request": The request is missing a required parameter,
includes an unsupported parameter or parameter value, repeats the
same parameter, uses more than one method for including an access
token, or is otherwise malformed. The resource server SHOULD
respond with the HTTP 400 (Bad Request) status code.
"invalid_token": The access token provided is expired, revoked,
malformed, or invalid for other reasons. The resource SHOULD
respond with the HTTP 401 (Unauthorized) status code. The client
MAY request a new access token and retry the protected resource
request.
Hardt, et al. Expires 8 September 2020 [Page 43]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
"insufficient_scope": The request requires higher privileges than
provided by the access token. The resource server SHOULD respond
with the HTTP 403 (Forbidden) status code and MAY include the
"scope" attribute with the scope necessary to access the protected
resource.
If the request lacks any authentication information (e.g., the client
was unaware that authentication is necessary or attempted using an
unsupported authentication method), the resource server SHOULD NOT
include an error code or other error information.
For example:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer realm="example"
7.4. Access Token Security Considerations
7.4.1. Security Threats
The following list presents several common threats against protocols
utilizing some form of tokens. This list of threats is based on NIST
Special Publication 800-63 [NIST800-63].
7.4.1.1. Token manufacture/modification
An attacker may generate a bogus token or modify the token contents
(such as the authentication or attribute statements) of an existing
token, causing the resource server to grant inappropriate access to
the client. For example, an attacker may modify the token to extend
the validity period; a malicious client may modify the assertion to
gain access to information that they should not be able to view.
7.4.1.2. Token disclosure
Tokens may contain authentication and attribute statements that
include sensitive information.
7.4.1.3. Token redirect
An attacker uses a token generated for consumption by one resource
server to gain access to a different resource server that mistakenly
believes the token to be for it.
7.4.1.4. Token replay
An attacker attempts to use a token that has already been used with
that resource server in the past.
Hardt, et al. Expires 8 September 2020 [Page 44]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
7.4.2. Threat Mitigation
A large range of threats can be mitigated by protecting the contents
of the token by using a digital signature. Alternatively, a bearer
token can contain a reference to authorization information, rather
than encoding the information directly. Such references MUST be
infeasible for an attacker to guess; using a reference may require an
extra interaction between a server and the token issuer to resolve
the reference to the authorization information. The mechanics of
such an interaction are not defined by this specification.
This document does not specify the encoding or the contents of the
token; hence, detailed recommendations about the means of
guaranteeing token integrity protection are outside the scope of this
document. The token integrity protection MUST be sufficient to
prevent the token from being modified.
To deal with token redirect, it is important for the authorization
server to include the identity of the intended recipients (the
audience), typically a single resource server (or a list of resource
servers), in the token. Restricting the use of the token to a
specific scope is also RECOMMENDED.
The authorization server MUST implement TLS. Which version(s) ought
to be implemented will vary over time and will depend on the
widespread deployment and known security vulnerabilities at the time
of implementation.
To protect against token disclosure, confidentiality protection MUST
be applied using TLS with a ciphersuite that provides confidentiality
and integrity protection. This requires that the communication
interaction between the client and the authorization server, as well
as the interaction between the client and the resource server,
utilize confidentiality and integrity protection. Since TLS is
mandatory to implement and to use with this specification, it is the
preferred approach for preventing token disclosure via the
communication channel. For those cases where the client is prevented
from observing the contents of the token, token encryption MUST be
applied in addition to the usage of TLS protection. As a further
defense against token disclosure, the client MUST validate the TLS
certificate chain when making requests to protected resources,
including checking the Certificate Revocation List (CRL) [RFC5280].
Cookies are typically transmitted in the clear. Thus, any
information contained in them is at risk of disclosure. Therefore,
Bearer tokens MUST NOT be stored in cookies that can be sent in the
clear, as any information in them is at risk of disclosure. See
Hardt, et al. Expires 8 September 2020 [Page 45]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
"HTTP State Management Mechanism" [RFC6265] for security
considerations about cookies.
In some deployments, including those utilizing load balancers, the
TLS connection to the resource server terminates prior to the actual
server that provides the resource. This could leave the token
unprotected between the front-end server where the TLS connection
terminates and the back-end server that provides the resource. In
such deployments, sufficient measures MUST be employed to ensure
confidentiality of the token between the front-end and back-end
servers; encryption of the token is one such possible measure.
To deal with token capture and replay, the following recommendations
are made: First, the lifetime of the token MUST be limited; one means
of achieving this is by putting a validity time field inside the
protected part of the token. Note that using short-lived (one hour
or less) tokens reduces the impact of them being leaked. Second,
confidentiality protection of the exchanges between the client and
the authorization server and between the client and the resource
server MUST be applied. As a consequence, no eavesdropper along the
communication path is able to observe the token exchange.
Consequently, such an on-path adversary cannot replay the token.
Furthermore, when presenting the token to a resource server, the
client MUST verify the identity of that resource server, as per
Section 3.1 of "HTTP Over TLS" [RFC2818]. Note that the client MUST
validate the TLS certificate chain when making these requests to
protected resources. Presenting the token to an unauthenticated and
unauthorized resource server or failing to validate the certificate
chain will allow adversaries to steal the token and gain unauthorized
access to protected resources.
7.4.3. Summary of Recommendations
7.4.3.1. Safeguard bearer tokens
Client implementations MUST ensure that bearer tokens are not leaked
to unintended parties, as they will be able to use them to gain
access to protected resources. This is the primary security
consideration when using bearer tokens and underlies all the more
specific recommendations that follow.
7.4.3.2. Validate TLS certificate chains
The client MUST validate the TLS certificate chain when making
requests to protected resources. Failing to do so may enable DNS
hijacking attacks to steal the token and gain unintended access.
Hardt, et al. Expires 8 September 2020 [Page 46]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
7.4.3.3. Always use TLS (https)
Clients MUST always use TLS (https) or equivalent transport security
when making requests with bearer tokens. Failing to do so exposes
the token to numerous attacks that could give attackers unintended
access.
7.4.3.4. Don't store bearer tokens in HTTP cookies
Implementations MUST NOT store bearer tokens within cookies that can
be sent in the clear (which is the default transmission mode for
cookies). Implementations that do store bearer tokens in cookies
MUST take precautions against cross-site request forgery.
7.4.3.5. Issue short-lived bearer tokens
Token servers SHOULD issue short-lived (one hour or less) bearer
tokens, particularly when issuing tokens to clients that run within a
web browser or other environments where information leakage may
occur. Using short-lived bearer tokens can reduce the impact of them
being leaked.
7.4.3.6. Issue scoped bearer tokens
Token servers SHOULD issue bearer tokens that contain an audience
restriction, scoping their use to the intended relying party or set
of relying parties.
7.4.3.7. Don't pass bearer tokens in page URLs
Bearer tokens MUST NOT be passed in page URLs (for example, as query
string parameters). Instead, bearer tokens SHOULD be passed in HTTP
message headers or message bodies for which confidentiality measures
are taken. Browsers, web servers, and other software may not
adequately secure URLs in the browser history, web server logs, and
other data structures. If bearer tokens are passed in page URLs,
attackers might be able to steal them from the history data, logs, or
other unsecured locations.
7.4.4. Token Replay Prevention
A sender-constrained access token scopes the applicability of an
access token to a certain sender. This sender is obliged to
demonstrate knowledge of a certain secret as prerequisite for the
acceptance of that token at the recipient (e.g., a resource server).
Authorization and resource servers SHOULD use mechanisms for sender-
constrained access tokens to prevent token replay as described in
Hardt, et al. Expires 8 September 2020 [Page 47]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
Section 4.8.1.1.2 of [I-D.ietf-oauth-security-topics]. The use of
Mutual TLS for OAuth 2.0 [RFC8705] is RECOMMENDED.
It is RECOMMENDED to use end-to-end TLS. If TLS traffic needs to be
terminated at an intermediary, refer to Section 4.11 of
[I-D.ietf-oauth-security-topics] for further security advice.
7.4.5. Access Token Privilege Restriction
The privileges associated with an access token SHOULD be restricted
to the minimum required for the particular application or use case.
This prevents clients from exceeding the privileges authorized by the
resource owner. It also prevents users from exceeding their
privileges authorized by the respective security policy. Privilege
restrictions also help to reduce the impact of access token leakage.
In particular, access tokens SHOULD be restricted to certain resource
servers (audience restriction), preferably to a single resource
server. To put this into effect, the authorization server associates
the access token with certain resource servers and every resource
server is obliged to verify, for every request, whether the access
token sent with that request was meant to be used for that particular
resource server. If not, the resource server MUST refuse to serve
the respective request. Clients and authorization servers MAY
utilize the parameters "scope" or "resource" as specified in this
document and [I-D.ietf-oauth-resource-indicators], respectively, to
determine the resource server they want to access.
Additionally, access tokens SHOULD be restricted to certain resources
and actions on resource servers or resources. To put this into
effect, the authorization server associates the access token with the
respective resource and actions and every resource server is obliged
to verify, for every request, whether the access token sent with that
request was meant to be used for that particular action on the
particular resource. If not, the resource server must refuse to
serve the respective request. Clients and authorization servers MAY
utilize the parameter "scope" and "authorization_details" as
specified in [I-D.ietf-oauth-rar] to determine those resources and/or
actions.
8. Extensibility
8.1. Defining Access Token Types
Access token types can be defined in one of two ways: registered in
the Access Token Types registry (following the procedures in
Section 12.1), or by using a unique absolute URI as its name.
Hardt, et al. Expires 8 September 2020 [Page 48]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
Types utilizing a URI name SHOULD be limited to vendor-specific
implementations that are not commonly applicable, and are specific to
the implementation details of the resource server where they are
used.
All other types MUST be registered. Type names MUST conform to the
type-name ABNF. If the type definition includes a new HTTP
authentication scheme, the type name SHOULD be identical to the HTTP
authentication scheme name (as defined by [RFC2617]). The token type
"example" is reserved for use in examples.
type-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
8.2. Defining New Endpoint Parameters
New request or response parameters for use with the authorization
endpoint or the token endpoint are defined and registered in the
OAuth Parameters registry following the procedure in Section 12.2.
Parameter names MUST conform to the param-name ABNF, and parameter
values syntax MUST be well-defined (e.g., using ABNF, or a reference
to the syntax of an existing parameter).
param-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
Unregistered vendor-specific parameter extensions that are not
commonly applicable and that are specific to the implementation
details of the authorization server where they are used SHOULD
utilize a vendor-specific prefix that is not likely to conflict with
other registered values (e.g., begin with 'companyname_').
8.3. Defining New Authorization Grant Types
New authorization grant types can be defined by assigning them a
unique absolute URI for use with the "grant_type" parameter. If the
extension grant type requires additional token endpoint parameters,
they MUST be registered in the OAuth Parameters registry as described
by Section 12.2.
8.4. Defining New Authorization Endpoint Response Types
New response types for use with the authorization endpoint are
defined and registered in the Authorization Endpoint Response Types
registry following the procedure in Section 12.3. Response type
names MUST conform to the response-type ABNF.
Hardt, et al. Expires 8 September 2020 [Page 49]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
response-type = response-name *( SP response-name )
response-name = 1*response-char
response-char = "_" / DIGIT / ALPHA
If a response type contains one or more space characters (%x20), it
is compared as a space-delimited list of values in which the order of
values does not matter. Only one order of values can be registered,
which covers all other arrangements of the same set of values.
For example, the response type "token code" is left undefined by this
specification. However, an extension can define and register the
"token code" response type. Once registered, the same combination
cannot be registered as "code token", but both values can be used to
denote the same response type.
8.5. Defining Additional Error Codes
In cases where protocol extensions (i.e., access token types,
extension parameters, or extension grant types) require additional
error codes to be used with the authorization code grant error
response (Section 4.1.2.1), the token error response (Section 5.2),
or the resource access error response (Section 7.3), such error codes
MAY be defined.
Extension error codes MUST be registered (following the procedures in
Section 12.4) if the extension they are used in conjunction with is a
registered access token type, a registered endpoint parameter, or an
extension grant type. Error codes used with unregistered extensions
MAY be registered.
Error codes MUST conform to the error ABNF and SHOULD be prefixed by
an identifying name when possible. For example, an error identifying
an invalid value set to the extension parameter "example" SHOULD be
named "example_invalid".
error = 1*error-char
error-char = %x20-21 / %x23-5B / %x5D-7E
9. Security Considerations
As a flexible and extensible framework, OAuth's security
considerations depend on many factors. The following sections
provide implementers with security guidelines focused on the three
client profiles described in Section 2.1: web application, browser-
based application, and native application.
A comprehensive OAuth security model and analysis, as well as
Hardt, et al. Expires 8 September 2020 [Page 50]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
background for the protocol design, is provided by [RFC6819] and
[I-D.ietf-oauth-security-topics].
9.1. Client Authentication
Authorization servers SHOULD use client authentication if possible.
It is RECOMMENDED to use asymmetric (public-key based) methods for
client authentication such as mTLS [RFC8705] or "private_key_jwt"
[OpenID]. When asymmetric methods for client authentication are
used, authorization servers do not need to store sensitive symmetric
keys, making these methods more robust against a number of attacks.
Authorization server MUST only rely on client authentication if the
process of issuance/registration and distribution of the underlying
credentials ensures their confidentiality.
When client authentication is not possible, the authorization server
SHOULD employ other means to validate the client's identity - for
example, by requiring the registration of the client redirection URI
or enlisting the resource owner to confirm identity. A valid
redirection URI is not sufficient to verify the client's identity
when asking for resource owner authorization but can be used to
prevent delivering credentials to a counterfeit client after
obtaining resource owner authorization.
The authorization server must consider the security implications of
interacting with unauthenticated clients and take measures to limit
the potential exposure of other credentials (e.g., refresh tokens)
issued to such clients.
The privileges an authorization server associates with a certain
client identity MUST depend on the assessment of the overall process
for client identification and client credential lifecycle management.
For example, authentication of a dynamically registered client just
ensures the authorization server it is talking to the same client
again. In contrast, if there is a web application whose developer's
identity was verified, who signed a contract and is issued a client
secret that is only used in a secure backend service, the
authorization server might allow this client to access more sensible
services or to use the client credential grant type.
Hardt, et al. Expires 8 September 2020 [Page 51]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
9.1.1. Client Authentication of Native Apps
Secrets that are statically included as part of an app distributed to
multiple users should not be treated as confidential secrets, as one
user may inspect their copy and learn the shared secret. For this
reason, it is NOT RECOMMENDED for authorization servers to require
client authentication of public native apps clients using a shared
secret, as this serves little value beyond client identification
which is already provided by the "client_id" request parameter.
Authorization servers that still require a statically included shared
secret for native app clients MUST treat the client as a public
client (as defined in Section 2.1), and not accept the secret as
proof of the client's identity. Without additional measures, such
clients are subject to client impersonation (see Section 9.3.1).
9.2. Registration of Native App Clients
Except when using a mechanism like Dynamic Client Registration
[RFC7591] to provision per-instance secrets, native apps are
classified as public clients, as defined in Section 2.1; they MUST be
registered with the authorization server as such. Authorization
servers MUST record the client type in the client registration
details in order to identify and process requests accordingly.
Authorization servers MUST require clients to register their complete
redirect URI (including the path component) and reject authorization
requests that specify a redirect URI that doesn't exactly match the
one that was registered; the exception is loopback redirects, where
an exact match is required except for the port URI component.
For private-use URI scheme-based redirects, authorization servers
SHOULD enforce the requirement in Section 10.3.1 that clients use
schemes that are reverse domain name based. At a minimum, any
private-use URI scheme that doesn't contain a period character (".")
SHOULD be rejected.
In addition to the collision-resistant properties, requiring a URI
scheme based on a domain name that is under the control of the app
can help to prove ownership in the event of a dispute where two apps
claim the same private-use URI scheme (where one app is acting
maliciously). For example, if two apps claimed "com.example.app",
the owner of "example.com" could petition the app store operator to
remove the counterfeit app. Such a petition is harder to prove if a
generic URI scheme was used.
Authorization servers MAY request the inclusion of other platform-
specific information, such as the app package or bundle name, or
Hardt, et al. Expires 8 September 2020 [Page 52]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
other information that may be useful for verifying the calling app's
identity on operating systems that support such functions.
9.3. Client Impersonation
A malicious client can impersonate another client and obtain access
to protected resources if the impersonated client fails to, or is
unable to, keep its client credentials confidential.
The authorization server MUST authenticate the client whenever
possible. If the authorization server cannot authenticate the client
due to the client's nature, the authorization server MUST require the
registration of any redirection URI used for receiving authorization
responses and SHOULD utilize other means to protect resource owners
from such potentially malicious clients. For example, the
authorization server can engage the resource owner to assist in
identifying the client and its origin.
The authorization server SHOULD enforce explicit resource owner
authentication and provide the resource owner with information about
the client and the requested authorization scope and lifetime. It is
up to the resource owner to review the information in the context of
the current client and to authorize or deny the request.
The authorization server SHOULD NOT process repeated authorization
requests automatically (without active resource owner interaction)
without authenticating the client or relying on other measures to
ensure that the repeated request comes from the original client and
not an impersonator.
9.3.1. Impersonation of Native Apps
As stated above, the authorization server SHOULD NOT process
authorization requests automatically without user consent or
interaction, except when the identity of the client can be assured.
This includes the case where the user has previously approved an
authorization request for a given client id - unless the identity of
the client can be proven, the request SHOULD be processed as if no
previous request had been approved.
Measures such as claimed "https" scheme redirects MAY be accepted by
authorization servers as identity proof. Some operating systems may
offer alternative platform-specific identity features that MAY be
accepted, as appropriate.
Hardt, et al. Expires 8 September 2020 [Page 53]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
9.4. Access Tokens
Access token credentials (as well as any confidential access token
attributes) MUST be kept confidential in transit and storage, and
only shared among the authorization server, the resource servers the
access token is valid for, and the client to whom the access token is
issued. Access token credentials MUST only be transmitted using TLS
as described in Section 1.6 with server authentication as defined by
[RFC2818].
The authorization server MUST ensure that access tokens cannot be
generated, modified, or guessed to produce valid access tokens by
unauthorized parties.
9.4.1. Access Token Privilege Restriction
The client SHOULD request access tokens with the minimal scope
necessary. The authorization server SHOULD take the client identity
into account when choosing how to honor the requested scope and MAY
issue an access token with less rights than requested.
The privileges associated with an access token SHOULD be restricted
to the minimum required for the particular application or use case.
This prevents clients from exceeding the privileges authorized by the
resource owner. It also prevents users from exceeding their
privileges authorized by the respective security policy. Privilege
restrictions also help to reduce the impact of access token leakage.
In particular, access tokens SHOULD be restricted to certain resource
servers (audience restriction), preferably to a single resource
server. To put this into effect, the authorization server associates
the access token with certain resource servers and every resource
server is obliged to verify, for every request, whether the access
token sent with that request was meant to be used for that particular
resource server. If not, the resource server MUST refuse to serve
the respective request. Clients and authorization servers MAY
utilize the parameters "scope" or "resource" as specified in
[RFC8707], respectively, to determine the resource server they want
to access.
9.4.2. Access Token Replay Prevention
Additionally, access tokens SHOULD be restricted to certain resources
and actions on resource servers or resources. To put this into
effect, the authorization server associates the access token with the
respective resource and actions and every resource server is obliged
to verify, for every request, whether the access token sent with that
request was meant to be used for that particular action on the
Hardt, et al. Expires 8 September 2020 [Page 54]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
particular resource. If not, the resource server must refuse to
serve the respective request. Clients and authorization servers MAY
utilize the parameter "scope" and "authorization_details" as
specified in [I-D.ietf-oauth-rar] to determine those resources and/or
actions.
Authorization and resource servers SHOULD use mechanisms for sender-
constrained access tokens to prevent token replay as described in
(#pop_tokens). A sender-constrained access token scopes the
applicability of an access token to a certain sender. This sender is
obliged to demonstrate knowledge of a certain secret as prerequisite
for the acceptance of that token at the recipient (e.g., a resource
server). The use of Mutual TLS for OAuth 2.0 [RFC8705] is
RECOMMENDED.
9.5. Refresh Tokens
Authorization servers MAY issue refresh tokens to clients.
Refresh tokens MUST be kept confidential in transit and storage, and
shared only among the authorization server and the client to whom the
refresh tokens were issued. The authorization server MUST maintain
the binding between a refresh token and the client to whom it was
issued. Refresh tokens MUST only be transmitted using TLS as
described in Section 1.6 with server authentication as defined by
[RFC2818].
The authorization server MUST verify the binding between the refresh
token and client identity whenever the client identity can be
authenticated. When client authentication is not possible, the
authorization server MUST issue sender-constrained refresh tokens or
use refresh token rotation as described in
(#refresh_token_protection).
The authorization server MUST ensure that refresh tokens cannot be
generated, modified, or guessed to produce valid refresh tokens by
unauthorized parties.
9.6. Protecting Redirect-Based Flows
When comparing client redirect URIs against pre-registered URIs,
authorization servers MUST utilize exact string matching. This
measure contributes to the prevention of leakage of authorization
codes and access tokens (see (#insufficient_uri_validation)). It can
also help to detect mix-up attacks (see (#mix_up)).
Clients MUST NOT expose URLs that forward the user's browser to
arbitrary URIs obtained from a query parameter ("open redirector").
Hardt, et al. Expires 8 September 2020 [Page 55]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
Open redirectors can enable exfiltration of authorization codes and
access tokens, see (#open_redirector_on_client).
Clients MUST prevent Cross-Site Request Forgery (CSRF). In this
context, CSRF refers to requests to the redirection endpoint that do
not originate at the authorization server, but a malicious third
party (see Section 4.4.1.8. of [RFC6819] for details). Clients that
have ensured that the authorization server supports PKCE MAY rely the
CSRF protection provided by PKCE. In OpenID Connect flows, the
"nonce" parameter provides CSRF protection. Otherwise, one-time use
CSRF tokens carried in the "state" parameter that are securely bound
to the user agent MUST be used for CSRF protection (see
(#csrf_countermeasures)).
In order to prevent mix-up attacks (see (#mix_up)), clients MUST only
process redirect responses of the authorization server they sent the
respective request to and from the same user agent this authorization
request was initiated with. Clients MUST store the authorization
server they sent an authorization request to and bind this
information to the user agent and check that the authorization
request was received from the correct authorization server. Clients
MUST ensure that the subsequent token request, if applicable, is sent
to the same authorization server. Clients SHOULD use distinct
redirect URIs for each authorization server as a means to identify
the authorization server a particular response came from.
An AS that redirects a request potentially containing user
credentials MUST avoid forwarding these user credentials accidentally
(see (#redirect_307) for details).
9.6.1. Loopback Redirect Considerations in Native Apps
Loopback interface redirect URIs use the "http" scheme (i.e., without
Transport Layer Security (TLS)). This is acceptable for loopback
interface redirect URIs as the HTTP request never leaves the device.
Clients should open the network port only when starting the
authorization request and close it once the response is returned.
Clients should listen on the loopback network interface only, in
order to avoid interference by other network actors.
While redirect URIs using localhost (i.e.,
"http://localhost:{port}/{path}") function similarly to loopback IP
redirects described in Section 10.3.3, the use of "localhost" is NOT
RECOMMENDED. Specifying a redirect URI with the loopback IP literal
rather than "localhost" avoids inadvertently listening on network
interfaces other than the loopback interface. It is also less
Hardt, et al. Expires 8 September 2020 [Page 56]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
susceptible to client-side firewalls and misconfigured host name
resolution on the user's device.
9.7. Authorization Codes
The transmission of authorization codes MUST be made over a secure
channel, and the client MUST require the use of TLS with its
redirection URI if the URI identifies a network resource. Since
authorization codes are transmitted via user-agent redirections, they
could potentially be disclosed through user-agent history and HTTP
referrer headers.
Authorization codes MUST be short lived and single-use. If the
authorization server observes multiple attempts to exchange an
authorization code for an access token, the authorization server
SHOULD attempt to revoke all refresh and access tokens already
granted based on the compromised authorization code.
If the client can be authenticated, the authorization servers MUST
authenticate the client and ensure that the authorization code was
issued to the same client.
Clients MUST prevent injection (replay) of authorization codes into
the authorization response by attackers. The use of PKCE is
RECOMMENDED to this end. The OpenID Connect "nonce" parameter and ID
Token Claim [OpenID] MAY be used as well. The PKCE challenge or
OpenID Connect "nonce" MUST be transaction-specific and securely
bound to the client and the user agent in which the transaction was
started.
Note: although PKCE so far was designed as a mechanism to protect
native apps, this advice applies to all kinds of OAuth clients,
including web applications.
When using PKCE, clients SHOULD use PKCE code challenge methods that
do not expose the PKCE verifier in the authorization request.
Otherwise, attackers that can read the authorization request (cf.
Attacker A4 in (#secmodel)) can break the security provided by PKCE.
Currently, "S256" is the only such method.
Authorization servers MUST support PKCE.
Authorization servers MUST provide a way to detect their support for
PKCE. To this end, they MUST either (a) publish the element
"code_challenge_methods_supported" in their AS metadata ([RFC8418])
containing the supported PKCE challenge methods (which can be used by
the client to detect PKCE support) or (b) provide a deployment-
specific way to ensure or determine PKCE support by the AS.
Hardt, et al. Expires 8 September 2020 [Page 57]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
9.8. Request Confidentiality
Access tokens, refresh tokens, authorization codes, and client
credentials MUST NOT be transmitted in the clear.
The "state" and "scope" parameters SHOULD NOT include sensitive
client or resource owner information in plain text, as they can be
transmitted over insecure channels or stored insecurely.
9.9. Ensuring Endpoint Authenticity
In order to prevent man-in-the-middle attacks, the authorization
server MUST require the use of TLS with server authentication as
defined by [RFC2818] for any request sent to the authorization and
token endpoints. The client MUST validate the authorization server's
TLS certificate as defined by [RFC6125] and in accordance with its
requirements for server identity authentication.
9.10. Credentials-Guessing Attacks
The authorization server MUST prevent attackers from guessing access
tokens, authorization codes, refresh tokens, resource owner
passwords, and client credentials.
The probability of an attacker guessing generated tokens (and other
credentials not intended for handling by end-users) MUST be less than
or equal to 2^(-128) and SHOULD be less than or equal to 2^(-160).
The authorization server MUST utilize other means to protect
credentials intended for end-user usage.
9.11. Phishing Attacks
Wide deployment of this and similar protocols may cause end-users to
become inured to the practice of being redirected to websites where
they are asked to enter their passwords. If end-users are not
careful to verify the authenticity of these websites before entering
their credentials, it will be possible for attackers to exploit this
practice to steal resource owners' passwords.
Service providers should attempt to educate end-users about the risks
phishing attacks pose and should provide mechanisms that make it easy
for end-users to confirm the authenticity of their sites. Client
developers should consider the security implications of how they
interact with the user-agent (e.g., external, embedded), and the
ability of the end-user to verify the authenticity of the
authorization server.
Hardt, et al. Expires 8 September 2020 [Page 58]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
To reduce the risk of phishing attacks, the authorization servers
MUST require the use of TLS on every endpoint used for end-user
interaction.
9.12. Fake External User-Agents in Native Apps
The native app that is initiating the authorization request has a
large degree of control over the user interface and can potentially
present a fake external user-agent, that is, an embedded user-agent
made to appear as an external user-agent.
When all good actors are using external user-agents, the advantage is
that it is possible for security experts to detect bad actors, as
anyone faking an external user-agent is provably bad. On the other
hand, if good and bad actors alike are using embedded user-agents,
bad actors don't need to fake anything, making them harder to detect.
Once a malicious app is detected, it may be possible to use this
knowledge to blacklist the app's signature in malware scanning
software, take removal action (in the case of apps distributed by app
stores) and other steps to reduce the impact and spread of the
malicious app.
Authorization servers can also directly protect against fake external
user-agents by requiring an authentication factor only available to
true external user-agents.
Users who are particularly concerned about their security when using
in-app browser tabs may also take the additional step of opening the
request in the full browser from the in-app browser tab and complete
the authorization there, as most implementations of the in-app
browser tab pattern offer such functionality.
9.13. Malicious External User-Agents in Native Apps
If a malicious app is able to configure itself as the default handler
for "https" scheme URIs in the operating system, it will be able to
intercept authorization requests that use the default browser and
abuse this position of trust for malicious ends such as phishing the
user.
This attack is not confined to OAuth; a malicious app configured in
this way would present a general and ongoing risk to the user beyond
OAuth usage by native apps. Many operating systems mitigate this
issue by requiring an explicit user action to change the default
handler for "http" and "https" scheme URIs.
Hardt, et al. Expires 8 September 2020 [Page 59]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
9.14. Cross-Site Request Forgery
An attacker might attempt to inject a request to the redirect URI of
the legitimate client on the victim's device, e.g., to cause the
client to access resources under the attacker's control. This is a
variant of an attack known as Cross-Site Request Forgery (CSRF).
The traditional countermeasure are CSRF tokens that are bound to the
user agent and passed in the "state" parameter to the authorization
server as described in [RFC6819]. The same protection is provided by
PKCE or the OpenID Connect "nonce" value.
When using PKCE instead of "state" or "nonce" for CSRF protection, it
is important to note that:
* Clients MUST ensure that the AS supports PKCE before using PKCE
for CSRF protection. If an authorization server does not support
PKCE, "state" or "nonce" MUST be used for CSRF protection.
* If "state" is used for carrying application state, and integrity
of its contents is a concern, clients MUST protect "state" against
tampering and swapping. This can be achieved by binding the
contents of state to the browser session and/or signed/encrypted
state values [I-D.bradley-oauth-jwt-encoded-state].
AS therefore MUST provide a way to detect their support for PKCE
either via AS metadata according to [RFC8414] or provide a
deployment-specific way to ensure or determine PKCE support.
9.15. Clickjacking
As described in Section 4.4.1.9 of [RFC6819], the authorization
request is susceptible to clickjacking. An attacker can use this
vector to obtain the user's authentication credentials, change the
scope of access granted to the client, and potentially access the
user's resources.
Authorization servers MUST prevent clickjacking attacks. Multiple
countermeasures are described in [RFC6819], including the use of the
X-Frame-Options HTTP response header field and frame-busting
JavaScript. In addition to those, authorization servers SHOULD also
use Content Security Policy (CSP) level 2 [CSP-2] or greater.
To be effective, CSP must be used on the authorization endpoint and,
if applicable, other endpoints used to authenticate the user and
authorize the client (e.g., the device authorization endpoint, login
pages, error pages, etc.). This prevents framing by unauthorized
origins in user agents that support CSP. The client MAY permit being
Hardt, et al. Expires 8 September 2020 [Page 60]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
framed by some other origin than the one used in its redirection
endpoint. For this reason, authorization servers SHOULD allow
administrators to configure allowed origins for particular clients
and/or for clients to register these dynamically.
Using CSP allows authorization servers to specify multiple origins in
a single response header field and to constrain these using flexible
patterns (see [CSP-2] for details). Level 2 of this standard
provides a robust mechanism for protecting against clickjacking by
using policies that restrict the origin of frames (using "frame-
ancestors") together with those that restrict the sources of scripts
allowed to execute on an HTML page (by using "script-src"). A non-
normative example of such a policy is shown in the following listing:
"HTTP/1.1 200 OK Content-Security-Policy: frame-ancestors
https://ext.example.org:8000 Content-Security-Policy: script-src
'self' X-Frame-Options: ALLOW-FROM https://ext.example.org:8000 ..."
Because some user agents do not support [CSP-2], this technique
SHOULD be combined with others, including those described in
[RFC6819], unless such legacy user agents are explicitly unsupported
by the authorization server. Even in such cases, additional
countermeasures SHOULD still be employed.
9.16. Code Injection and Input Validation
A code injection attack occurs when an input or otherwise external
variable is used by an application unsanitized and causes
modification to the application logic. This may allow an attacker to
gain access to the application device or its data, cause denial of
service, or introduce a wide range of malicious side-effects.
The authorization server and client MUST sanitize (and validate when
possible) any value received - in particular, the value of the
"state" and "redirect_uri" parameters.
9.17. Open Redirectors
The following attacks can occur when an AS or client has an open
redirector. An open redirector is an endpoint that forwards a user's
browser to an arbitrary URI obtained from a query parameter.
Hardt, et al. Expires 8 September 2020 [Page 61]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
9.17.1. Client as Open Redirector
Clients MUST NOT expose open redirectors. Attackers may use open
redirectors to produce URLs pointing to the client and utilize them
to exfiltrate authorization codes and access tokens, as described in
(#redir_uri_open_redir). Another abuse case is to produce URLs that
appear to point to the client. This might trick users into trusting
the URL and follow it in their browser. This can be abused for
phishing.
In order to prevent open redirection, clients should only redirect if
the target URLs are whitelisted or if the origin and integrity of a
request can be authenticated. Countermeasures against open
redirection are described by OWASP [owasp_redir].
9.17.2. Authorization Server as Open Redirector
Just as with clients, attackers could try to utilize a user's trust
in the authorization server (and its URL in particular) for
performing phishing attacks. OAuth authorization servers regularly
redirect users to other web sites (the clients), but must do so in a
safe way.
Section 4.1.2.1 already prevents open redirects by stating that the
AS MUST NOT automatically redirect the user agent in case of an
invalid combination of "client_id" and "redirect_uri".
However, an attacker could also utilize a correctly registered
redirect URI to perform phishing attacks. The attacker could, for
example, register a client via dynamic client registration [RFC7591]
and intentionally send an erroneous authorization request, e.g., by
using an invalid scope value, thus instructing the AS to redirect the
user agent to its phishing site.
The AS MUST take precautions to prevent this threat. Based on its
risk assessment, the AS needs to decide whether it can trust the
redirect URI and SHOULD only automatically redirect the user agent if
it trusts the redirect URI. If the URI is not trusted, the AS MAY
inform the user and rely on the user to make the correct decision.
9.18. Authorization Server Mix-Up Mitigation in Native Apps
(TODO: merge this with the regular mix-up section when it is brought
in)
To protect against a compromised or malicious authorization server
attacking another authorization server used by the same app, it is
REQUIRED that a unique redirect URI is used for each authorization
Hardt, et al. Expires 8 September 2020 [Page 62]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
server used by the app (for example, by varying the path component),
and that authorization responses are rejected if the redirect URI
they were received on doesn't match the redirect URI in an outgoing
authorization request.
The native app MUST store the redirect URI used in the authorization
request with the authorization session data (i.e., along with "state"
and other related data) and MUST verify that the URI on which the
authorization response was received exactly matches it.
The requirement of Section 9.2, specifically that authorization
servers reject requests with URIs that don't match what was
registered, is also required to prevent such attacks.
9.19. Embedded User Agents in Native Apps
Embedded user-agents are a technically possible method for
authorizing native apps. These embedded user-agents are unsafe for
use by third parties to the authorization server by definition, as
the app that hosts the embedded user-agent can access the user's full
authentication credential, not just the OAuth authorization grant
that was intended for the app.
In typical web-view-based implementations of embedded user-agents,
the host application can record every keystroke entered in the login
form to capture usernames and passwords, automatically submit forms
to bypass user consent, and copy session cookies and use them to
perform authenticated actions as the user.
Even when used by trusted apps belonging to the same party as the
authorization server, embedded user-agents violate the principle of
least privilege by having access to more powerful credentials than
they need, potentially increasing the attack surface.
Encouraging users to enter credentials in an embedded user-agent
without the usual address bar and visible certificate validation
features that browsers have makes it impossible for the user to know
if they are signing in to the legitimate site; even when they are, it
trains them that it's OK to enter credentials without validating the
site first.
Aside from the security concerns, embedded user-agents do not share
the authentication state with other apps or the browser, requiring
the user to log in for every authorization request, which is often
considered an inferior user experience.
Hardt, et al. Expires 8 September 2020 [Page 63]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
9.20. Other Recommendations
Authorization servers SHOULD NOT allow clients to influence their
"client_id" or "sub" value or any other claim if that can cause
confusion with a genuine resource owner (see
(#client_impersonating)).
10. Native Applications
Native applications are clients installed and executed on the device
used by the resource owner (i.e., desktop application, native mobile
application). Native applications require special consideration
related to security, platform capabilities, and overall end-user
experience.
The authorization endpoint requires interaction between the client
and the resource owner's user-agent. The best current practice is to
perform the OAuth authorization request in an external user-agent
(typically the browser) rather than an embedded user-agent (such as
one implemented with web-views).
The native application can capture the response from the
authorization server using a redirection URI with a scheme registered
with the operating system to invoke the client as the handler, manual
copy-and-paste of the credentials, running a local web server,
installing a user-agent extension, or by providing a redirection URI
identifying a server-hosted resource under the client's control,
which in turn makes the response available to the native application.
Previously, it was common for native apps to use embedded user-agents
(commonly implemented with web-views) for OAuth authorization
requests. That approach has many drawbacks, including the host app
being able to copy user credentials and cookies as well as the user
needing to authenticate from scratch in each app. See Section 9.19
for a deeper analysis of the drawbacks of using embedded user-agents
for OAuth.
Native app authorization requests that use the browser are more
secure and can take advantage of the user's authentication state.
Being able to use the existing authentication session in the browser
enables single sign-on, as users don't need to authenticate to the
authorization server each time they use a new app (unless required by
the authorization server policy).
Supporting authorization flows between a native app and the browser
is possible without changing the OAuth protocol itself, as the OAuth
authorization request and response are already defined in terms of
URIs. This encompasses URIs that can be used for inter-app
Hardt, et al. Expires 8 September 2020 [Page 64]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
communication. Some OAuth server implementations that assume all
clients are confidential web clients will need to add an
understanding of public native app clients and the types of redirect
URIs they use to support this best practice.
10.1. Using Inter-App URI Communication for OAuth in Native Apps
Just as URIs are used for OAuth on the web to initiate the
authorization request and return the authorization response to the
requesting website, URIs can be used by native apps to initiate the
authorization request in the device's browser and return the response
to the requesting native app.
By adopting the same methods used on the web for OAuth, benefits seen
in the web context like the usability of a single sign-on session and
the security of a separate authentication context are likewise gained
in the native app context. Reusing the same approach also reduces
the implementation complexity and increases interoperability by
relying on standards-based web flows that are not specific to a
particular platform.
Native apps MUST use an external user-agent to perform OAuth
authorization requests. This is achieved by opening the
authorization request in the browser (detailed in Section 10.2) and
using a redirect URI that will return the authorization response back
to the native app (defined in Section 10.3).
10.2. Initiating the Authorization Request from a Native App
Native apps needing user authorization create an authorization
request URI with the authorization code grant type per Section 4.1
using a redirect URI capable of being received by the native app.
The function of the redirect URI for a native app authorization
request is similar to that of a web-based authorization request.
Rather than returning the authorization response to the OAuth
client's server, the redirect URI used by a native app returns the
response to the app. Several options for a redirect URI that will
return the authorization response to the native app in different
platforms are documented in Section 10.3. Any redirect URI that
allows the app to receive the URI and inspect its parameters is
viable.
After constructing the authorization request URI, the app uses
platform-specific APIs to open the URI in an external user-agent.
Typically, the external user-agent used is the default browser, that
is, the application configured for handling "http" and "https" scheme
Hardt, et al. Expires 8 September 2020 [Page 65]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
URIs on the system; however, different browser selection criteria and
other categories of external user-agents MAY be used.
This best practice focuses on the browser as the RECOMMENDED external
user-agent for native apps. An external user-agent designed
specifically for user authorization and capable of processing
authorization requests and responses like a browser MAY also be used.
Other external user-agents, such as a native app provided by the
authorization server may meet the criteria set out in this best
practice, including using the same redirection URI properties, but
their use is out of scope for this specification.
Some platforms support a browser feature known as "in-app browser
tabs", where an app can present a tab of the browser within the app
context without switching apps, but still retain key benefits of the
browser such as a shared authentication state and security context.
On platforms where they are supported, it is RECOMMENDED, for
usability reasons, that apps use in-app browser tabs for the
authorization request.
10.3. Receiving the Authorization Response in a Native App
There are several redirect URI options available to native apps for
receiving the authorization response from the browser, the
availability and user experience of which varies by platform.
To fully support native apps, authorization servers MUST offer at
least the three redirect URI options described in the following
subsections to native apps. Native apps MAY use whichever redirect
option suits their needs best, taking into account platform-specific
implementation details.
10.3.1. Private-Use URI Scheme Redirection
Many mobile and desktop computing platforms support inter-app
communication via URIs by allowing apps to register private-use URI
schemes (sometimes colloquially referred to as "custom URL schemes")
like "com.example.app". When the browser or another app attempts to
load a URI with a private-use URI scheme, the app that registered it
is launched to handle the request.
To perform an authorization request with a private-use URI scheme
redirect, the native app launches the browser with a standard
authorization request, but one where the redirection URI utilizes a
private-use URI scheme it registered with the operating system.
When choosing a URI scheme to associate with the app, apps MUST use a
URI scheme based on a domain name under their control, expressed in
Hardt, et al. Expires 8 September 2020 [Page 66]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
reverse order, as recommended by Section 3.8 of [RFC7595] for
private-use URI schemes.
For example, an app that controls the domain name "app.example.com"
can use "com.example.app" as their scheme. Some authorization
servers assign client identifiers based on domain names, for example,
"client1234.usercontent.example.net", which can also be used as the
domain name for the scheme when reversed in the same manner. A
scheme such as "myapp", however, would not meet this requirement, as
it is not based on a domain name.
When there are multiple apps by the same publisher, care must be
taken so that each scheme is unique within that group. On platforms
that use app identifiers based on reverse-order domain names, those
identifiers can be reused as the private-use URI scheme for the OAuth
redirect to help avoid this problem.
Following the requirements of Section 3.2 of [RFC3986], as there is
no naming authority for private-use URI scheme redirects, only a
single slash ("/") appears after the scheme component. A complete
example of a redirect URI utilizing a private-use URI scheme is:
com.example.app:/oauth2redirect/example-provider
When the authorization server completes the request, it redirects to
the client's redirection URI as it would normally. As the
redirection URI uses a private-use URI scheme, it results in the
operating system launching the native app, passing in the URI as a
launch parameter. Then, the native app uses normal processing for
the authorization response.
10.3.2. Claimed "https" Scheme URI Redirection
Some operating systems allow apps to claim "https" scheme [RFC7230]
URIs in the domains they control. When the browser encounters a
claimed URI, instead of the page being loaded in the browser, the
native app is launched with the URI supplied as a launch parameter.
Such URIs can be used as redirect URIs by native apps. They are
indistinguishable to the authorization server from a regular web-
based client redirect URI. An example is:
https://app.example.com/oauth2redirect/example-provider
As the redirect URI alone is not enough to distinguish public native
app clients from confidential web clients, it is REQUIRED in
Section 9.2 that the client type be recorded during client
Hardt, et al. Expires 8 September 2020 [Page 67]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
registration to enable the server to determine the client type and
act accordingly.
App-claimed "https" scheme redirect URIs have some advantages
compared to other native app redirect options in that the identity of
the destination app is guaranteed to the authorization server by the
operating system. For this reason, native apps SHOULD use them over
the other options where possible.
10.3.3. Loopback Interface Redirection
Native apps that are able to open a port on the loopback network
interface without needing special permissions (typically, those on
desktop operating systems) can use the loopback interface to receive
the OAuth redirect.
Loopback redirect URIs use the "http" scheme and are constructed with
the loopback IP literal and whatever port the client is listening on.
That is, "http://127.0.0.1:{port}/{path}" for IPv4, and
"http://[::1]:{port}/{path}" for IPv6. An example redirect using the
IPv4 loopback interface with a randomly assigned port:
http://127.0.0.1:51004/oauth2redirect/example-provider
An example redirect using the IPv6 loopback interface with a randomly
assigned port:
http://[::1]:61023/oauth2redirect/example-provider
The authorization server MUST allow any port to be specified at the
time of the request for loopback IP redirect URIs, to accommodate
clients that obtain an available ephemeral port from the operating
system at the time of the request.
Clients SHOULD NOT assume that the device supports a particular
version of the Internet Protocol. It is RECOMMENDED that clients
attempt to bind to the loopback interface using both IPv4 and IPv6
and use whichever is available.
11. Browser-Based Apps
Browser-based apps are are clients that run in a web browser,
typically written in JavaScript, also known as "single-page apps".
These types of apps have particular security considerations similar
to native apps.
Hardt, et al. Expires 8 September 2020 [Page 68]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
TODO: Bring in the normative text of the browser-based apps BCP when
it is finalized.
12. IANA Considerations
12.1. OAuth Access Token Types Registry
This specification establishes the OAuth Access Token Types registry.
Access token types are registered with a Specification Required
([RFC5226]) after a two-week review period on the oauth-ext-
review@ietf.org mailing list, on the advice of one or more Designated
Experts. However, to allow for the allocation of values prior to
publication, the Designated Expert(s) may approve registration once
they are satisfied that such a specification will be published.
Registration requests must be sent to the oauth-ext-review@ietf.org
mailing list for review and comment, with an appropriate subject
(e.g., "Request for access token type: example").
Within the review period, the Designated Expert(s) will either
approve or deny the registration request, communicating this decision
to the review list and IANA. Denials should include an explanation
and, if applicable, suggestions as to how to make the request
successful.
IANA must only accept registry updates from the Designated Expert(s)
and should direct all requests for registration to the review mailing
list.
12.1.1. Registration Template
Type name: The name requested (e.g., "example").
Additional Token Endpoint Response Parameters: Additional response
parameters returned together with the "access_token" parameter.
New parameters MUST be separately registered in the OAuth
Parameters registry as described by Section 12.2.
HTTP Authentication Scheme(s): The HTTP authentication scheme
name(s), if any, used to authenticate protected resource requests
using access tokens of this type.
Change controller: For Standards Track RFCs, state "IETF". For
others, give the name of the responsible party. Other details
(e.g., postal address, email address, home page URI) may also be
included.
Hardt, et al. Expires 8 September 2020 [Page 69]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
Specification document(s): Reference to the document(s) that specify
the parameter, preferably including a URI that can be used to
retrieve a copy of the document(s). An indication of the relevant
sections may also be included but is not required.
12.1.2. Initial Registry Contents
The OAuth Access Token Types registry's initial contents are:
* Type name: Bearer
* Additional Token Endpoint Response Parameters: (none)
* HTTP Authentication Scheme(s): Bearer
* Change controller: IETF
* Specification document(s): OAuth 2.1
12.2. OAuth Parameters Registry
This specification establishes the OAuth Parameters registry.
Additional parameters for inclusion in the authorization endpoint
request, the authorization endpoint response, the token endpoint
request, or the token endpoint response are registered with a
Specification Required ([RFC5226]) after a two-week review period on
the oauth-ext-review@ietf.org mailing list, on the advice of one or
more Designated Experts. However, to allow for the allocation of
values prior to publication, the Designated Expert(s) may approve
registration once they are satisfied that such a specification will
be published.
Registration requests must be sent to the oauth-ext-review@ietf.org
mailing list for review and comment, with an appropriate subject
(e.g., "Request for parameter: example").
Within the review period, the Designated Expert(s) will either
approve or deny the registration request, communicating this decision
to the review list and IANA. Denials should include an explanation
and, if applicable, suggestions as to how to make the request
successful.
IANA must only accept registry updates from the Designated Expert(s)
and should direct all requests for registration to the review mailing
list.
Hardt, et al. Expires 8 September 2020 [Page 70]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
12.2.1. Registration Template
Parameter name: The name requested (e.g., "example").
Parameter usage location: The location(s) where parameter can be
used. The possible locations are authorization request,
authorization response, token request, or token response.
Change controller: For Standards Track RFCs, state "IETF". For
others, give the name of the responsible party. Other details
(e.g., postal address, email address, home page URI) may also be
included.
Specification document(s): Reference to the document(s) that specify
the parameter, preferably including a URI that can be used to
retrieve a copy of the document(s). An indication of the relevant
sections may also be included but is not required.
12.2.2. Initial Registry Contents
The OAuth Parameters registry's initial contents are:
* Parameter name: client_id
* Parameter usage location: authorization request, token request
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: client_secret
* Parameter usage location: token request
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: response_type
* Parameter usage location: authorization request
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: redirect_uri
Hardt, et al. Expires 8 September 2020 [Page 71]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
* Parameter usage location: authorization request, token request
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: scope
* Parameter usage location: authorization request, authorization
response, token request, token response
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: state
* Parameter usage location: authorization request, authorization
response
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: code
* Parameter usage location: authorization response, token request
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: error_description
* Parameter usage location: authorization response, token response
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: error_uri
* Parameter usage location: authorization response, token response
* Change controller: IETF
* Specification document(s): RFC 6749
Hardt, et al. Expires 8 September 2020 [Page 72]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
* Parameter name: grant_type
* Parameter usage location: token request
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: access_token
* Parameter usage location: authorization response, token response
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: token_type
* Parameter usage location: authorization response, token response
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: expires_in
* Parameter usage location: authorization response, token response
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: username
* Parameter usage location: token request
* Change controller: IETF
* Specification document(s): RFC 6749
* Parameter name: password
* Parameter usage location: token request
* Change controller: IETF
* Specification document(s): RFC 6749
Hardt, et al. Expires 8 September 2020 [Page 73]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
* Parameter name: refresh_token
* Parameter usage location: token request, token response
* Change controller: IETF
* Specification document(s): RFC 6749
12.3. OAuth Authorization Endpoint Response Types Registry
This specification establishes the OAuth Authorization Endpoint
Response Types registry.
Additional response types for use with the authorization endpoint are
registered with a Specification Required ([RFC5226]) after a two-week
review period on the oauth-ext-review@ietf.org mailing list, on the
advice of one or more Designated Experts. However, to allow for the
allocation of values prior to publication, the Designated Expert(s)
may approve registration once they are satisfied that such a
specification will be published.
Registration requests must be sent to the oauth-ext-review@ietf.org
mailing list for review and comment, with an appropriate subject
(e.g., "Request for response type: example").
Within the review period, the Designated Expert(s) will either
approve or deny the registration request, communicating this decision
to the review list and IANA. Denials should include an explanation
and, if applicable, suggestions as to how to make the request
successful.
IANA must only accept registry updates from the Designated Expert(s)
and should direct all requests for registration to the review mailing
list.
12.3.1. Registration Template
Response type name: The name requested (e.g., "example").
Change controller: For Standards Track RFCs, state "IETF". For
others, give the name of the responsible party. Other details
(e.g., postal address, email address, home page URI) may also be
included.
Specification document(s): Reference to the document(s) that specify
the type, preferably including a URI that can be used to retrieve
a copy of the document(s). An indication of the relevant sections
may also be included but is not required.
Hardt, et al. Expires 8 September 2020 [Page 74]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
12.3.2. Initial Registry Contents
The OAuth Authorization Endpoint Response Types registry's initial
contents are:
* Response type name: code
* Change controller: IETF
* Specification document(s): RFC 6749
12.4. OAuth Extensions Error Registry
This specification establishes the OAuth Extensions Error registry.
Additional error codes used together with other protocol extensions
(i.e., extension grant types, access token types, or extension
parameters) are registered with a Specification Required ([RFC5226])
after a two-week review period on the oauth-ext-review@ietf.org
mailing list, on the advice of one or more Designated Experts.
However, to allow for the allocation of values prior to publication,
the Designated Expert(s) may approve registration once they are
satisfied that such a specification will be published.
Registration requests must be sent to the oauth-ext-review@ietf.org
mailing list for review and comment, with an appropriate subject
(e.g., "Request for error code: example").
Within the review period, the Designated Expert(s) will either
approve or deny the registration request, communicating this decision
to the review list and IANA. Denials should include an explanation
and, if applicable, suggestions as to how to make the request
successful.
IANA must only accept registry updates from the Designated Expert(s)
and should direct all requests for registration to the review mailing
list.
12.4.1. Registration Template
Error name: The name requested (e.g., "example"). Values for the
error name MUST NOT include characters outside the set %x20-21 /
%x23-5B / %x5D-7E.
Error usage location: The location(s) where the error can be used.
The possible locations are authorization code grant error response
(Section 4.1.2.1), token error response (Section 5.2), or resource
access error response (Section 7.3).
Hardt, et al. Expires 8 September 2020 [Page 75]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
Related protocol extension: The name of the extension grant type,
access token type, or extension parameter that the error code is
used in conjunction with.
Change controller: For Standards Track RFCs, state "IETF". For
others, give the name of the responsible party. Other details
(e.g., postal address, email address, home page URI) may also be
included.
Specification document(s): Reference to the document(s) that specify
the error code, preferably including a URI that can be used to
retrieve a copy of the document(s). An indication of the relevant
sections may also be included but is not required.
12.4.2. Initial Registry Contents
The OAuth Error registry's initial contents are:
* Error name: invalid_request
* Error usage location: Resource access error response
* Change controller: IETF
* Specification document(s): OAuth 2.1
* Error name: invalid_token
* Error usage location: Resource access error response
* Change controller: IETF
* Specification document(s): OAuth 2.1
* Error name: insufficient_scope
* Error usage location: Resource access error response
* Change controller: IETF
* Specification document(s): OAuth 2.1
13. References
13.1. Normative References
[I-D.ietf-oauth-security-topics]
Lodderstedt, T., Bradley, J., Labunets, A., and D. Fett,
Hardt, et al. Expires 8 September 2020 [Page 76]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
"OAuth 2.0 Security Best Current Practice", Work in
Progress, Internet-Draft, draft-ietf-oauth-security-
topics-14, 10 February 2020, <http://www.ietf.org/
internet-drafts/draft-ietf-oauth-security-topics-14.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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,
DOI 10.17487/RFC2616, June 1999,
<https://www.rfc-editor.org/info/rfc2616>.
[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, DOI 10.17487/RFC2617, June 1999,
<https://www.rfc-editor.org/info/rfc2617>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627,
DOI 10.17487/RFC4627, July 2006,
<https://www.rfc-editor.org/info/rfc4627>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
Hardt, et al. Expires 8 September 2020 [Page 77]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<https://www.rfc-editor.org/info/rfc6750>.
[RFC7595] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines
and Registration Procedures for URI Schemes", BCP 35,
RFC 7595, DOI 10.17487/RFC7595, June 2015,
<https://www.rfc-editor.org/info/rfc7595>.
[RFC8252] Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps",
BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017,
<https://www.rfc-editor.org/info/rfc8252>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[USASCII] Institute, A.N.S., "Coded Character Set -- 7-bit American
Standard Code for Information Interchange, ANSI X3.4",
1986.
[W3C.REC-html401-19991224]
Raggett, D., Hors, A., and I. Jacobs, "HTML 4.01
Specification", World Wide Web Consortium Recommendation
Hardt, et al. Expires 8 September 2020 [Page 78]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
REC-html401-19991224, 24 December 1999,
<http://www.w3.org/TR/1999/REC-html401-19991224>.
[W3C.REC-xml-20081126]
Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, 26 November 2008,
<http://www.w3.org/TR/2008/REC-xml-20081126>.
13.2. Informative References
[CSP-2] "Content Security Policy Level 2", December 2016,
<https://www.w3.org/TR/CSP2>.
[I-D.bradley-oauth-jwt-encoded-state]
Bradley, J., Lodderstedt, T., and H. Zandbelt, "Encoding
claims in the OAuth 2 state parameter using a JWT", Work
in Progress, Internet-Draft, draft-bradley-oauth-jwt-
encoded-state-09, 4 November 2018, <http://www.ietf.org/
internet-drafts/draft-bradley-oauth-jwt-encoded-state-
09.txt>.
[I-D.ietf-oauth-browser-based-apps]
Parecki, A. and D. Waite, "OAuth 2.0 for Browser-Based
Apps", Work in Progress, Internet-Draft, draft-ietf-oauth-
browser-based-apps-05, 28 February 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-oauth-
browser-based-apps-05.txt>.
[I-D.ietf-oauth-rar]
Lodderstedt, T., Richer, J., and B. Campbell, "OAuth 2.0
Rich Authorization Requests", Work in Progress, Internet-
Draft, draft-ietf-oauth-rar-01, 19 February 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-oauth-rar-
01.txt>.
[I-D.ietf-oauth-resource-indicators]
Campbell, B., Bradley, J., and H. Tschofenig, "Resource
Indicators for OAuth 2.0", Work in Progress, Internet-
Draft, draft-ietf-oauth-resource-indicators-08, 11
September 2019, <http://www.ietf.org/internet-drafts/
draft-ietf-oauth-resource-indicators-08.txt>.
[I-D.ietf-oauth-token-binding]
Jones, M., Campbell, B., Bradley, J., and W. Denniss,
"OAuth 2.0 Token Binding", Work in Progress, Internet-
Draft, draft-ietf-oauth-token-binding-08, 19 October 2018,
Hardt, et al. Expires 8 September 2020 [Page 79]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
<http://www.ietf.org/internet-drafts/draft-ietf-oauth-
token-binding-08.txt>.
[NIST800-63]
Burr, W., Dodson, D., Newton, E., Perlner, R., Polk, T.,
Gupta, S., and E. Nabbus, "NIST Special Publication
800-63-1, INFORMATION SECURITY", December 2011,
<http://csrc.nist.gov/publications/>.
[OMAP] Huff, J., Schlacht, D., Nadalin, A., Simmons, J.,
Rosenberg, P., Madsen, P., Ace, T., Rickelton-Abdi, C.,
and B. Boyer, "Online Multimedia Authorization Protocol:
An Industry Standard for Authorized Access to Internet
Multimedia Resources", April 2012,
<https://www.oatc.us/Standards/Download-Standards>.
[OpenID] Sakimora, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0", November 2014,
<https://openiD.net/specs/openiD-connect-core-1_0.html>.
[OpenID.Messages]
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B.,
Mortimore, C., and E. Jay, "OpenID Connect Messages 1.0",
June 2012, <http://openid.net/specs/openid-connect-
messages-1_0.html>.
[owasp_redir]
"OWASP Cheat Sheet Series - Unvalidated Redirects and
Forwards", 2020,
<https://cheatsheetseries.owasp.org/cheatsheets/
Unvalidated_Redirects_and_Forwards_Cheat_Sheet.html>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>.
[RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0
Threat Model and Security Considerations", RFC 6819,
DOI 10.17487/RFC6819, January 2013,
<https://www.rfc-editor.org/info/rfc6819>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Authentication", RFC 7235,
Hardt, et al. Expires 8 September 2020 [Page 80]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
DOI 10.17487/RFC7235, June 2014,
<https://www.rfc-editor.org/info/rfc7235>.
[RFC7522] Campbell, B., Mortimore, C., and M. Jones, "Security
Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0
Client Authentication and Authorization Grants", RFC 7522,
DOI 10.17487/RFC7522, May 2015,
<https://www.rfc-editor.org/info/rfc7522>.
[RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
RFC 7591, DOI 10.17487/RFC7591, July 2015,
<https://www.rfc-editor.org/info/rfc7591>.
[RFC7636] Sakimura, N., Ed., Bradley, J., and N. Agarwal, "Proof Key
for Code Exchange by OAuth Public Clients", RFC 7636,
DOI 10.17487/RFC7636, September 2015,
<https://www.rfc-editor.org/info/rfc7636>.
[RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", RFC 8414,
DOI 10.17487/RFC8414, June 2018,
<https://www.rfc-editor.org/info/rfc8414>.
[RFC8418] Housley, R., "Use of the Elliptic Curve Diffie-Hellman Key
Agreement Algorithm with X25519 and X448 in the
Cryptographic Message Syntax (CMS)", RFC 8418,
DOI 10.17487/RFC8418, August 2018,
<https://www.rfc-editor.org/info/rfc8418>.
[RFC8705] Campbell, B., Bradley, J., Sakimura, N., and T.
Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
and Certificate-Bound Access Tokens", RFC 8705,
DOI 10.17487/RFC8705, February 2020,
<https://www.rfc-editor.org/info/rfc8705>.
[RFC8707] Campbell, B., Bradley, J., and H. Tschofenig, "Resource
Indicators for OAuth 2.0", RFC 8707, DOI 10.17487/RFC8707,
February 2020, <https://www.rfc-editor.org/info/rfc8707>.
Appendix A. Augmented Backus-Naur Form (ABNF) Syntax
This section provides Augmented Backus-Naur Form (ABNF) syntax
descriptions for the elements defined in this specification using the
notation of [RFC5234]. The ABNF below is defined in terms of Unicode
code points [W3C.REC-xml-20081126]; these characters are typically
encoded in UTF-8. Elements are presented in the order first defined.
Hardt, et al. Expires 8 September 2020 [Page 81]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
Some of the definitions that follow use the "URI-reference"
definition from [RFC3986].
Some of the definitions that follow use these common definitions:
VSCHAR = %x20-7E
NQCHAR = %x21 / %x23-5B / %x5D-7E
NQSCHAR = %x20-21 / %x23-5B / %x5D-7E
UNICODECHARNOCRLF = %x09 /%x20-7E / %x80-D7FF /
%xE000-FFFD / %x10000-10FFFF
(The UNICODECHARNOCRLF definition is based upon the Char definition
in Section 2.2 of [W3C.REC-xml-20081126], but omitting the Carriage
Return and Linefeed characters.)
A.1. "client_id" Syntax
The "client_id" element is defined in Section 2.3.1:
client-id = *VSCHAR
A.2. "client_secret" Syntax
The "client_secret" element is defined in Section 2.3.1:
client-secret = *VSCHAR
A.3. "response_type" Syntax
The "response_type" element is defined in Section 3.1.1 and
Section 8.4:
response-type = response-name *( SP response-name )
response-name = 1*response-char
response-char = "_" / DIGIT / ALPHA
A.4. "scope" Syntax
The "scope" element is defined in Section 3.3:
scope = scope-token *( SP scope-token )
scope-token = 1*NQCHAR
A.5. "state" Syntax
The "state" element is defined in Section 4.1.1, Section 4.1.2, and
Section 4.1.2.1:
Hardt, et al. Expires 8 September 2020 [Page 82]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
state = 1*VSCHAR
A.6. "redirect_uri" Syntax
The "redirect_uri" element is defined in Section 4.1.1, and
Section 4.1.3:
redirect-uri = URI-reference
A.7. "error" Syntax
The "error" element is defined in Sections Section 4.1.2.1,
Section 5.2, 7.2, and 8.5:
error = 1*NQSCHAR
A.8. "error_description" Syntax
The "error_description" element is defined in Sections
Section 4.1.2.1, Section 5.2, and Section 7.3:
error-description = 1*NQSCHAR
A.9. "error_uri" Syntax
The "error_uri" element is defined in Sections Section 4.1.2.1,
Section 5.2, and 7.2:
error-uri = URI-reference
A.10. "grant_type" Syntax
The "grant_type" element is defined in Sections Section 4.1.3,
Section 4.2.3, Section 4.2.2, Section 4.3, and Section 6:
grant-type = grant-name / URI-reference
grant-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
A.11. "code" Syntax
The "code" element is defined in Section 4.1.3:
code = 1*VSCHAR
Hardt, et al. Expires 8 September 2020 [Page 83]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
A.12. "access_token" Syntax
The "access_token" element is defined in Section 4.2.3 and
Section 5.1:
access-token = 1*VSCHAR
A.13. "token_type" Syntax
The "token_type" element is defined in Section 5.1, and Section 8.1:
token-type = type-name / URI-reference
type-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
A.14. "expires_in" Syntax
The "expires_in" element is defined in Section 5.1:
expires-in = 1*DIGIT
A.15. "refresh_token" Syntax
The "refresh_token" element is defined in Section 5.1 and Section 6:
refresh-token = 1*VSCHAR
A.16. Endpoint Parameter Syntax
The syntax for new endpoint parameters is defined in Section 8.2:
param-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
A.17. "code_verifier" Syntax
ABNF for "code_verifier" is as follows.
code-verifier = 43*128unreserved
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
ALPHA = %x41-5A / %x61-7A
DIGIT = %x30-39
A.18. "code_challenge" Syntax
ABNF for "code_challenge" is as follows.
Hardt, et al. Expires 8 September 2020 [Page 84]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
code-challenge = 43*128unreserved
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
ALPHA = %x41-5A / %x61-7A
DIGIT = %x30-39
Appendix B. Use of application/x-www-form-urlencoded Media Type
At the time of publication of this specification, the "application/x-
www-form-urlencoded" media type was defined in Section 17.13.4 of
[W3C.REC-html401-19991224] but not registered in the IANA MIME Media
Types registry (http://www.iana.org/assignments/media-types
(http://www.iana.org/assignments/media-types)). Furthermore, that
definition is incomplete, as it does not consider non-US-ASCII
characters.
To address this shortcoming when generating payloads using this media
type, names and values MUST be encoded using the UTF-8 character
encoding scheme [RFC3629] first; the resulting octet sequence then
needs to be further encoded using the escaping rules defined in
[W3C.REC-html401-19991224].
When parsing data from a payload using this media type, the names and
values resulting from reversing the name/value encoding consequently
need to be treated as octet sequences, to be decoded using the UTF-8
character encoding scheme.
For example, the value consisting of the six Unicode code points (1)
U+0020 (SPACE), (2) U+0025 (PERCENT SIGN), (3) U+0026 (AMPERSAND),
(4) U+002B (PLUS SIGN), (5) U+00A3 (POUND SIGN), and (6) U+20AC (EURO
SIGN) would be encoded into the octet sequence below (using
hexadecimal notation):
20 25 26 2B C2 A3 E2 82 AC
and then represented in the payload as:
+%25%26%2B%C2%A3%E2%82%AC
Appendix C. Acknowledgements
TBD
Authors' Addresses
Dick Hardt
SignIn.Org
United States
Hardt, et al. Expires 8 September 2020 [Page 85]
Internet-Draft The OAuth 2.1 Authorization Framework March 2020
Email: dick.hardt@gmail.com
Aaron Parecki
Okta
United States
Email: aaron@parecki.com
URI: https://aaronparecki.com
Torsten Lodderstedt
yes.com
Email: torsten@lodderstedt.net
Hardt, et al. Expires 8 September 2020 [Page 86]