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Security Web Authorization Protocol oauth refresh token consent token endpoint This specification extends OAuth 2.0 by adding new token endpoint response parameters to specify refresh token expiration and user consent expiration. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Web Authorization Protocol Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction RFC6749 defines the OAuth 2.0 protocol, part of which is the ability for a client to receive a refresh token that may be repeatedly exchanged for more access tokens. OAuth 2.0 does not contain any normative language around expiration or lack thereof for refresh tokens, mentioning only that they are "typically long-lasting". In the years since the publication of OAuth 2.0, in response to changing security and privacy landscapes, many authorization servers have begun to issue shorter-lived refresh tokens for two main reasons:

• The authorization server or user may decide that the access being granted is too sensitive to allow indefinite access (e.g. mail or health data).
• The authorization server enforces a maximum duration that refresh tokens may be held without rotation. [OAuth 2.1 Sec 4.3.1]

Clients may wish to implement special handling for expiring refresh tokens. For example, if the user has granted expiring access, the client may notify the user that they will need to reauthorize access before a certain date to avoid interruption of service.

Requirements Notation and Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Terminology "Resource owner" and "user" may be used interchangeably to refer to the entity capable of granting access to a protected resource. "Client", "application", and "relying party" may be used interchangeably to refer to the application making protected resource requests on behalf of the resource owner and with its authorization.

Concepts There are two mechanisms that can affect refresh token expiration.

Consent expiration When granting consent for an application to access their data, the user may opt to time-limit that consent, especially if the data is sensitive or they aren't sure how long they'll continue using the application. The authorization server itself may also impose mandatory limits on consent duration.

Refresh token rotation Authorization servers implementing refresh token rotation may wish to define a maximum amount of time clients can hold a refresh token without rotating it. Beyond the security benefit provided by expiring credentials, this also provides a convenient mechanism for authorization servers to change refresh token keys without having to accept old credentials forever.

Refresh token expiration The refresh token MUST expire no later than the user consent expires. It MAY expire earlier if the authorization server also enforces a maximum duration between refresh token rotations. If the user renews their consent, the authorization server MAY update the expiration time of existing refresh tokens if their lifetime was truncated due to user consent expiration. The authorization server MUST NOT accept expired refresh tokens for any purpose, even if it has no way to update the expiration time of existing refresh tokens.

Token endpoint response This specification introduces two new response parameters.

Successful response

Infinite Expiration Omitted values indicate that there is no fixed upper bound on the lifetime of the credential or consent. If the authorization server has not declared its support for refresh token lifetime in the Authorization Server Metadata, omitted response fields could indicate either indefinite validity or simply lack of support for this specification. However, infinite expiration and lack of information about expiration should be handled by the client in the same way. That is to say, the client must always handle refresh token invalidation not caused by expiration, such as by explicit user revocation. Rather than omitting a response value, an authorization server may choose to return a large arbitrary value, e.g. "315569520" for 10 years. This avoids any ambiguity around support for infinite values while achieving a similar practical effect. Clients MUST treat all large values as literals and MUST NOT make any assumptions about which may be considered infinite.

Error response The existing invalid_grant error code already explicitly covers token expiration and should be sufficient. Upon receiving this error code the client SHOULD start a new authorization grant flow.

Example Suppose an authorization server enforces that refresh tokens must be rotated at least once every 7 days, and a user has granted consent to an application for access for 30 days. The initial exchange will result in the following response values: An exchange 7 days after initial authorization will result in the following response values: An exchange 28 days after initial authorization will result in the following response values:

Update to Authorization Server Metadata Support for the expiring refresh tokens SHOULD be declared in the OAuth 2.0 Authorization Server Metadata with the following metadata: If the authorization server omits expiration time response fields to indicate indefinite validity, it MUST declare refresh_token_expiration_types in its metadata to indicate to the client that it's aware of this spec.

Security Considerations While it is possible to allow refresh token expiration to exceed that of user consent expiration if the authorization server checks both timestamps when validating a refresh token, this is a potentially dangerous source of bugs in systems with complicated user consent models. By requiring refresh tokens to expire no later than user consent expires, there is less risk of bugs that accidentally provide data access to the client beyond the term of the user's consent.

Privacy Considerations Allowing users to time-limit their consent is a privacy improvement. While this was already doable in regular OAuth implementations, the potential interruption of service for the user may have discouraged implementation of the feature. This specification provides a standardized way to mitigate that concern and should lead to greater adoption of time-limited consent.

IANA Considerations

OAuth Parameters Registration This specification registers the following OAuth parameter definitions in the IANA OAuth Parameters registry.

Registry Contents

• Name: refresh_token_expires_in
  • Parameter Usage Location: token response
  • Change Controller: IETF
  • Reference: This document
• Name: consent_expires_in
  • Parameter Usage Location: token response
  • Change Controller: IETF
  • Reference: This document

OAuth Authorization Server Metadata Registration This specification registers the following Authorization Server Metadata definitions in the IANA OAuth Authorization Server Metadata registry.

Registry Contents

• Metadata Name: refresh_token_expiration_types
  • Metadata Description: What types of refresh token expiration are supported by the authorization server
  • Change Controller: IETF
  • Reference: This document

Normative References The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. This specification replaces and obsoletes the OAuth 1.0 protocol described in RFC 5849. [STANDARDS-TRACK] This specification defines a metadata format that an OAuth 2.0 client can use to obtain the information needed to interact with an OAuth 2.0 authorization server, including its endpoint locations and authorization server capabilities. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.

Acknowledgments TODO acknowledge.