wdiff rfc9749v1.txt rfc9749.txt

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) WebPush Web Push

Abstract

This document defines a method for JSON Meta Application Protocol
(JMAP) servers to advertise their capability to authenticate WebPush 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.

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
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 WebPush 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 WebPush Web Push 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.

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"
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 Annex A Section 2.3.3 of
[X9.62])
[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 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 WebPush. Web Push. The security
considerations for JMAP [RFC8620] (especially Sections 8.6 and 8.7),
WebPush
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 186-4, 186-5,
DOI 10.6028/NIST.FIPS.186-4, July 2013,
<https://doi.org/10.6028/NIST.FIPS.186-4>.

[X9.62] American National 10.6028/NIST.FIPS.186-5, February 2023,
<https://doi.org/10.6028/NIST.FIPS.186-5>.

[SEC1] Standards Institute, "Public Key
Cryptography for the Financial Services Industry: The Efficient Cryptography Group, "SEC 1:
Elliptic Curve Digital Signature Algorithm (ECDSA)",
ANSI X9.62-2005, November 2005. 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