Use of VAPID in JMAP WebPush
draft-ietf-jmap-webpush-vapid-10

JMAP                                                          D. Gultsch
Internet-Draft                                           10 January 2025
Intended status: Standards Track                                        
Expires: 14 July 2025

                      Use of VAPID in JMAP WebPush
                    draft-ietf-jmap-webpush-vapid-10

Abstract

   This document defines a method for JMAP servers to advertise their
   capability to authenticate WebPush notifications using the Voluntary
   Application Server Identification protocol.

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 14 July 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.

Gultsch                   Expires 14 July 2025                  [Page 1]
Internet-Draft        Use of VAPID in JMAP WebPush          January 2025

Table of Contents

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

1.  Introduction

   JMAP [RFC8620] specifies how clients can subscribe to events using a
   protocol that is compatible with WebPush [RFC8030].  Some push
   services require that the application server authenticates all push
   messages using the Voluntary Application Server Identification
   protocol [RFC8292].  To facilitate that, the client (or user agent in
   WebPush terminology) needs the VAPID public key of the application
   server to pass it 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.  These words may also appear in this
   document in lower case as plain English words, absent their normative
   meanings.

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"

Gultsch                   Expires 14 July 2025                  [Page 2]
Internet-Draft        Use of VAPID in JMAP WebPush          January 2025

      The ECDSA public key that the push service will use to
      authenticate the application server, in its uncompressed form (as
      described in [X9.62] Annex A) 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 ([PUSH-API],
   Section 7.2), allowing the key to be directly copied and used without
   additional transformation.  Additionally, as noted in [RFC8292],
   Section 3.2, the X9.62 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 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.

Gultsch                   Expires 14 July 2025                  [Page 3]
Internet-Draft        Use of VAPID in JMAP WebPush          January 2025

   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 [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 HTTP status code 403, as specified in
   [RFC8292], Section 4.2.

   Per the requirements of [RFC8620], Section 7.2, 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 the 'Key
   Rotation' section 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 Voluntary Application Server
   Identification (VAPID).  This property does not reveal sensitive
   information, nor does it introduce new security or privacy risks
   beyond those inherent to JMAP and WebPush.  The security
   considerations for JMAP ([RFC8620], especially Section 8.6 and
   Section 8.7 of that document), WebPush ([RFC8030]) and VAPID
   ([RFC8292]) apply to this document.

7.  IANA Considerations

Gultsch                   Expires 14 July 2025                  [Page 4]
Internet-Draft        Use of VAPID in JMAP WebPush          January 2025

7.1.  Registration of the JMAP Capability for VAPID

   This specification requests IANA to register a new capability in the
   JMAP Capabilities registry with the following data:

   Capability Name: urn:ietf:params:jmap:webpush-vapid

   Specification document: this document

   Intended use: common

   Change Controller: IETF

   Security and privacy considerations: this document, Section 6

8.  References

8.1.  Normative References

   [FIPS186]  National Institute of Standards and Technology (NIST),
              "Digital Signature Standard (DSS)", FIPS 186-4, July 2013,
              <https://doi.org/10.6028/NIST.FIPS.186-4>.

   [X9.62]    American National Standards Institute, "Public Key
              Cryptography for the Financial Services Industry: The
              Elliptic Curve Digital Signature Algorithm (ECDSA)",
              ANSI X9.62-2005, November 2005.

   [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>.

Gultsch                   Expires 14 July 2025                  [Page 5]
Internet-Draft        Use of VAPID in JMAP WebPush          January 2025

   [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] Peter Beverloo, Martin Thomson, and Marcos Caceres, "Push
              API", September 2024, <https://www.w3.org/TR/push-api/>.

Author's Address

   Daniel Gultsch
   Email: daniel@gultsch.de

Gultsch                   Expires 14 July 2025                  [Page 6]