JMAP Web Push VAPID: Use of Voluntary Application Server Identification (VAPID) in JSON Meta Application Protocol (JMAP) Web Push

Internet Engineering Task Force (IETF)                        D. Gultsch
Request for Comments: 9749                                    March 2025
Category: Standards Track
ISSN: 2070-1721


Use of Voluntary Application Server Identification (VAPID) in JSON Meta
                  Application Protocol (JMAP) Web Push

Abstract

   This document defines a method for JSON Meta Application Protocol
   (JMAP) servers to advertise their capability to authenticate Web Push
   notifications using the Voluntary Application Server Identification
   (VAPID) protocol.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9749.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
   3.  Discovering Support for VAPID
   4.  Issuing Push Notifications
   5.  Key Rotation
   6.  Security Considerations
   7.  IANA Considerations
     7.1.  Registration of the JMAP Capability for VAPID
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Author's Address

1.  Introduction

   JMAP [RFC8620] specifies how clients can subscribe to events using a
   protocol that is compatible with Web Push [RFC8030].  Some push
   services require that the application server authenticate all push
   messages using the VAPID protocol [RFC8292].  To facilitate that, the
   client (or user agent in Web Push terminology) needs the VAPID public
   key of the application server to pass along to the push service when
   retrieving a new endpoint.

2.  Conventions Used in This Document

   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.  Discovering Support for VAPID

   The JMAP capabilities object is returned as part of the standard JMAP
   session object (see Section 2 of [RFC8620]).  Servers supporting this
   specification MUST add a property called
   urn:ietf:params:jmap:webpush-vapid to the capabilities object.  The
   value of this property is an object that MUST contain the following
   information:

   applicationServerKey: "String"
      The Elliptic Curve Digital Signature Algorithm (ECDSA) public key
      that the push service will use to authenticate the application
      server, in its uncompressed form (as described in Section 2.3.3 of
      [SEC1]) and encoded using base64url encoding [RFC7515].  Current
      systems use the P-256 curve [FIPS186].

      |  Informative Note: The format of the application server key was
      |  chosen to ensure compatibility with the browser API
      |  (Section 7.2 of [PUSH-API]), allowing the key to be directly
      |  copied and used without additional transformation.
      |  Additionally, as noted in Section 3.2 of [RFC8292], the X9.62
      |  encoding (which is compatible with SEC1 encoding) simplifies
      |  key comparisons and is more compact than alternative formats.

4.  Issuing Push Notifications

   Every time the server sends a push message to a PushSubscription URL,
   it MUST authenticate the POST request using the protocol outlined in
   [RFC8292].  This includes both StateChange events and
   PushVerification notifications.  To authenticate the request, the
   server MUST use a JSON Web Token (JWT) signed by the private key
   corresponding to the application server key.  This application server
   key MUST be the one that was advertised in the capabilities object at
   the time the PushSubscription was created.

5.  Key Rotation

   When a server needs to replace its VAPID key, it MUST update the
   sessionState per [RFC8620].  The client MUST monitor the JMAP session
   object for changes to the VAPID key and MUST recreate its push
   subscription when it detects such a change.

   After key rotation, the server MAY continue to send push
   notifications for existing push subscriptions using the old
   application server key for a transitional period.  This allows
   clients time to recreate their respective push subscriptions.  At the
   end of the transitional period (or immediately for implementations
   that do not have one), the server MUST destroy push subscriptions
   that use the old key.

   When destroying push subscriptions that include the data type
   PushSubscription, the server MAY issue one final StateChange push
   notification using the old URL and application server key to notify
   the client of changes to the PushSubscription data type.  This
   prompts the client to make a PushSubscription/changes method call.
   The response to this call will contain an updated sessionState, which
   refers to a session object that contains the new VAPID key.

   A race condition can occur when the server updates its VAPID key
   after the client has refreshed the session object but before calling
   the PushSubscription/set method.  This situation causes the server to
   send a PushVerification object to a push resource URL that is now
   associated with an outdated VAPID key.  Consequently, the push
   service will reject the PushVerification with a 403 (Forbidden)
   status code, as specified in Section 4.2 of [RFC8292].

   To alleviate this problem, the client MUST check if the sessionState
   in the response from the PushSubscription/set method points to a
   session object with an applicationServerKey that matches their
   expectations.  If there is a mismatch, the client MAY retry creating
   the PushSubscription.  Additionally, the client MAY destroy the
   PushSubscription from the earlier, failed attempt.

6.  Security Considerations

   During the key rotation process, synchronization issues between the
   client and server may arise.  Specifically, a client might restrict a
   push subscription with the push service to an outdated key, while the
   server sends the PushVerification object authenticated with the newly
   rotated key.  This mismatch leads to the push service rejecting the
   PushVerification request with a 403 (Forbidden) status code, as
   specified in Section 4.2 of [RFC8292].

   Per the requirements of Section 7.2 of [RFC8620], the server MUST NOT
   retry the rejected PushVerification request.  Consequently, the
   PushVerification object will not be delivered to the client.

   To mitigate such issues, the client is responsible for detecting and
   resolving any synchronization discrepancies, as outlined in Section 5
   of this document.

   The inclusion of the urn:ietf:params:jmap:webpush-vapid property in
   the JMAP capabilities object is limited to providing information
   about the server's support for VAPID.  This property does not reveal
   sensitive information, nor does it introduce new security or privacy
   risks beyond those inherent to JMAP and Web Push.  The security
   considerations for JMAP [RFC8620] (especially Sections 8.6 and 8.7),
   Web Push [RFC8030], and VAPID [RFC8292] apply to this document.

7.  IANA Considerations

7.1.  Registration of the JMAP Capability for VAPID

   IANA has registered the following new capability in the "JMAP
   Capabilities" registry:

   Capability Name:  urn:ietf:params:jmap:webpush-vapid
   Intended Use:  common
   Change Controller:  IETF
   Security and Privacy Considerations:  RFC 9749, Section 6
   Reference:  RFC 9749

8.  References

8.1.  Normative References

   [FIPS186]  NIST, "Digital Signature Standard (DSS)", NIST FIPS 186-5,
              DOI 10.6028/NIST.FIPS.186-5, February 2023,
              <https://doi.org/10.6028/NIST.FIPS.186-5>.

   [SEC1]     Standards for Efficient Cryptography Group, "SEC 1:
              Elliptic Curve Cryptography", Version 2.0, May 2009,
              <http://www.secg.org/sec1-v2.pdf>.

   [RFC8620]  Jenkins, N. and C. Newman, "The JSON Meta Application
              Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July
              2019, <https://www.rfc-editor.org/info/rfc8620>.

   [RFC8030]  Thomson, M., Damaggio, E., and B. Raymor, Ed., "Generic
              Event Delivery Using HTTP Push", RFC 8030,
              DOI 10.17487/RFC8030, December 2016,
              <https://www.rfc-editor.org/info/rfc8030>.

   [RFC8292]  Thomson, M. and P. Beverloo, "Voluntary Application Server
              Identification (VAPID) for Web Push", RFC 8292,
              DOI 10.17487/RFC8292, November 2017,
              <https://www.rfc-editor.org/info/rfc8292>.

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

8.2.  Informative References

   [PUSH-API] Beverloo, P., Ed., Thomson, M., Ed., and M. Caceres, Ed.,
              "Push API", W3C Working Draft, September 2024,
              <https://www.w3.org/TR/push-api/>.

Author's Address

   Daniel Gultsch
   Email: daniel@gultsch.de