Web Authorization Protocol N. Watson Internet-Draft Google, LLC Intended status: Informational 27 June 2025 Expires: 29 December 2025 OAuth 2.0 Refresh Token and Consent Expiration draft-watson-oauth-refresh-token-expiration-00 Abstract This specification extends OAuth 2.0 [RFC6749] by adding new token endpoint response parameters to specify refresh token expiration and user consent expiration. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://njwatson32.github.io/rt-expiration/draft-watson-oauth- refresh-token-expiration.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-watson-oauth- refresh-token-expiration/. Discussion of this document takes place on the Web Authorization Protocol Working Group mailing list (mailto:oauth@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/oauth/. Subscribe at https://www.ietf.org/mailman/listinfo/oauth/. Source for this draft and an issue tracker can be found at https://github.com/njwatson32/rt-expiration. 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." Watson Expires 29 December 2025 [Page 1] Internet-Draft OAuth RT/Consent Expiration June 2025 This Internet-Draft will expire on 29 December 2025. Copyright Notice Copyright (c) 2025 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 and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Notation and Conventions . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.1. Consent expiration . . . . . . . . . . . . . . . . . . . 4 4.2. Refresh token rotation . . . . . . . . . . . . . . . . . 4 5. Refresh token expiration . . . . . . . . . . . . . . . . . . 4 6. Token endpoint response . . . . . . . . . . . . . . . . . . . 4 6.1. Successful response . . . . . . . . . . . . . . . . . . . 4 6.1.1. Infinite Expiration . . . . . . . . . . . . . . . . . 5 6.2. Error response . . . . . . . . . . . . . . . . . . . . . 5 6.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Update to Authorization Server Metadata . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 10.1. OAuth Parameters Registration . . . . . . . . . . . . . 6 10.1.1. Registry Contents . . . . . . . . . . . . . . . . . 6 10.2. OAuth Authorization Server Metadata Registration . . . . 7 10.2.1. Registry Contents . . . . . . . . . . . . . . . . . 7 11. Normative References . . . . . . . . . . . . . . . . . . . . 7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 Watson Expires 29 December 2025 [Page 2] Internet-Draft OAuth RT/Consent Expiration June 2025 1. 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. 2. 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. 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. 4. Concepts There are two mechanisms that can affect refresh token expiration. Watson Expires 29 December 2025 [Page 3] Internet-Draft OAuth RT/Consent Expiration June 2025 4.1. 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. 4.2. 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. 5. 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. 6. Token endpoint response This specification introduces two new response parameters. 6.1. Successful response refresh_token_expires_in The lifetime in seconds of the refresh token. For example, the value "604800" denotes that the refresh token will expire in one week from the time the response was generated. This value SHALL NOT exceed the value in consent_expires_in. consent_expires_in The lifetime in seconds of the user's consent. For example, the value "2629800" denotes that the consent will expire in one month from the time the response was generated. This value MAY exceed that of refresh_token_expires_in. Watson Expires 29 December 2025 [Page 4] Internet-Draft OAuth RT/Consent Expiration June 2025 6.1.1. 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. 6.2. 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. 6.3. 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: refresh_token_expires_in: "604800" // 7 days consent_expires_in: "2592000" // 30 days An exchange 7 days after initial authorization will result in the following response values: refresh_token_expires_in: "604800" // 7 days consent_expires_in: "1987200" // 23 days An exchange 28 days after initial authorization will result in the following response values: refresh_token_expires_in: "172800" // 2 days consent_expires_in: "172800" // 2 days Watson Expires 29 December 2025 [Page 5] Internet-Draft OAuth RT/Consent Expiration June 2025 7. Update to Authorization Server Metadata Support for the expiring refresh tokens SHOULD be declared in the OAuth 2.0 Authorization Server Metadata [RFC8414] with the following metadata: refresh_token_expiration_types OPTIONAL. JSON array of supported expiration types. The possible values are "consent" and "credential". 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. 8. 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. 9. 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. 10. IANA Considerations 10.1. OAuth Parameters Registration This specification registers the following OAuth parameter definitions in the IANA OAuth Parameters registry. 10.1.1. Registry Contents * Name: refresh_token_expires_in - Parameter Usage Location: token response - Change Controller: IETF Watson Expires 29 December 2025 [Page 6] Internet-Draft OAuth RT/Consent Expiration June 2025 - Reference: This document * Name: consent_expires_in - Parameter Usage Location: token response - Change Controller: IETF - Reference: This document 10.2. OAuth Authorization Server Metadata Registration This specification registers the following Authorization Server Metadata definitions in the IANA OAuth Authorization Server Metadata registry. 10.2.1. 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 11. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, October 2012, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0 Authorization Server Metadata", RFC 8414, DOI 10.17487/RFC8414, June 2018, . Watson Expires 29 December 2025 [Page 7] Internet-Draft OAuth RT/Consent Expiration June 2025 Acknowledgments TODO acknowledge. Author's Address Nicholas Watson Google, LLC Email: nwatson@google.com Watson Expires 29 December 2025 [Page 8]