Network Working Group S. Gougeon Internet-Draft 24 January 2025 Intended status: Informational Expires: 28 July 2025 The IMAP WEBPUSH extension draft-gougeon-imap-webpush-00 Abstract This document defines a WEBPUSH extension of the Internet Message Access Protocol (IMAP) that permits IMAP servers to send WebPush notifications. 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 28 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. Gougeon Expires 28 July 2025 [Page 1] Internet-Draft The IMAP WEBPUSH extension January 2025 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Client Commands . . . . . . . . . . . . . . . . . . . . . . . 3 4.1. GETVAPID Command . . . . . . . . . . . . . . . . . . . . 3 4.2. WEBPUSH Command . . . . . . . . . . . . . . . . . . . . . 4 4.3. LWEBPUSH Command . . . . . . . . . . . . . . . . . . . . 5 5. Server Responses . . . . . . . . . . . . . . . . . . . . . . 6 5.1. VAPID Response . . . . . . . . . . . . . . . . . . . . . 6 5.2. WEBPUSH Response . . . . . . . . . . . . . . . . . . . . 6 5.3. SYNC Response . . . . . . . . . . . . . . . . . . . . . . 7 6. Push notifications . . . . . . . . . . . . . . . . . . . . . 7 6.1. Content . . . . . . . . . . . . . . . . . . . . . . . . . 7 6.2. Push server response . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction WebPush (defined by [RFC8030], [RFC8291] and [RFC8292]) defines a way for applications to deliver real-time events in a timely fashion, with push notifications. Push notifications allows consolidating all real-time events into a single session which ensures more efficient use of network and radio resources. They are particularly used in mobile environments. Many use cases have led to a need for real-time events with email. IMAP support for real-time events has been added with the IDLE command ([RFC2177], [RFC9051]) and the NOTIFY extension ([RFC5465]). These commands require using a persistent connection per account and contribute to unnecessary use of the device radio. JMAP ([RFC8620]) has responded to this need by supporting WebPush from the beginning. Therefore, this extension permits IMAP servers to send WebPush notifications. Gougeon Expires 28 July 2025 [Page 2] Internet-Draft The IMAP WEBPUSH extension January 2025 2. Conventions and Definitions In examples, "C:" and "S:" indicate lines sent by the client and server, respectively. Lines ending in "\" are interrupted for presentation reasons, they would actually be joined to the next line. Note that each other line includes the terminating CRLF. User agent, is defined in [RFC8030] as a device and software that is the recipient of push messages. It describes here the mail client. 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. Overview This extension adds 3 commands: GETVAPID, WEBPUSH and LWEBPUSH. GETVAPID allows to get the server VAPID public key, WEBPUSH to subscribe a new push registration and LWEBPUSH to list current registrations. Every time a message is added to one of the subscribed mailbox (with the SUBSCRIBE command), the IMAP server sends a push message to the registered push endpoints. 4. Client Commands 4.1. GETVAPID Command Arguments: none Responses: REQUIRED untagged response: VAPID Result: OK - capability completed BAD - arguments invalid The GETVAPID command requests the VAPID public key ([RFC8292]) of the server. the server MUST send a single untagged VAPID response before the tagged OK response. This is used by clients to request a push endpoint on their push server restricted to this mail server. Example: Gougeon Expires 28 July 2025 [Page 3] Internet-Draft The IMAP WEBPUSH extension January 2025 C: a1 GETVAPID S: * VAPID \ "BOniQ9xHBPNY9gnQW4o-16vHqOb40pEIMifyUdFsxAgy\ zVkFMguxw0QrdbZcq8hRjN2zpeInRvKVPlkzABvuTnI" S: a1 OK GETVAPID completed 4.2. WEBPUSH Command Arguments (create/update): registration ID push endpoint ECDH public key authentication secret Arguments (delete): registration ID NIL Responses: OPTIONAL untagged response: WEBPUSH Result: OK - create completed NO - create failure: can't create webpush registration with these arguments BAD - command unknown or arguments invalid The VAPID command creates, updates or delete a push registration for the account. The server MAY return a single untagged VAPID response before the tagged OK response. The registration ID is uniq per account and identify the push registration. Sending a VAPID command with an existing registration ID updates the current registration. Sending a VAPID command with an existing registration ID following by NIL deletes the registration. The push endpoint MUST be the URI that the mail server sends push messages to. This is defined as the URI for push resource in [RFC8030]. This URI MUST use the "https" scheme. The ECDH public key is the user agent public key on the P-256 curve. It MUST be encoded in the uncompressed form [SEC_1] (section 2.3.3, replicated from X9.62), and base64url encoded as described in [RFC7515]. This is used to encrypt push notifications following [RFC8291]. Gougeon Expires 28 July 2025 [Page 4] Internet-Draft The IMAP WEBPUSH extension January 2025 The authentication secret is 16 random bytes. It MUST be base64url encoded as described in [RFC7515]. This is the salt used to encrypt push notifications following [RFC8291]. The client SHOULD register their push subscription from time to time, like when the client starts in order to restore registrations, in case the endpoint was removed. Example: C: a1 LWEBPUSH "*" S: a1 OK LWEBPUSH completed C: a2 WEBPUSH a8282bf9-6102-4e1b-bb61-d26d0e532e65 \ https://push.example.net/push/random1 \ BCVxsr7N_eNgVRqvHtD0zTZsEc6-VV-JvLexhqUzORcxaOzi6-AYWXvTBHm4bj\ yPjs7Vd8pZGH6SRpkNtoIAiw4 \ BTBZMqHH6r4Tts7J_aSIgg S: * WEBPUSH "a8282bf9-6102-4e1b-bb61-d26d0e532e65" \ "https://push.example.net/push/random1" S: a2 OK WEBPUSH completed C: a3 WEBPUSH a8282bf9-6102-4e1b-bb61-d26d0e532e65 \ https://push.example.net/push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV \ BCVxsr7N_eNgVRqvHtD0zTZsEc6-VV-JvLexhqUzORcxaOzi6-AYWXvTBHm4bj\ yPjs7Vd8pZGH6SRpkNtoIAiw4 \ BTBZMqHH6r4Tts7J_aSIgg S: * WEBPUSH "a8282bf9-6102-4e1b-bb61-d26d0e532e65" \ "https://push.example.net/push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV" S: a3 OK WEBPUSH completed C: a4 LWEBPUSH "*" S: * WEBPUSH "a8282bf9-6102-4e1b-bb61-d26d0e532e65" \ "https://push.example.net/push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV" S: a4 OK LWEBPUSH completed C: a5 WEBPUSH a8282bf9-6102-4e1b-bb61-d26d0e532e65 NIL S: a5 OK WEBPUSH completed C: a6 LWEBPUSH "*" S: a6 OK LWEBPUSH completed 4.3. LWEBPUSH Command Arguments: registration ID with possible wildcards Responses: untagged response: WEBPUSH Result: OK - list completed NO - list failure: can't list webpush records BAD - arguments invalid Gougeon Expires 28 July 2025 [Page 5] Internet-Draft The IMAP WEBPUSH extension January 2025 The LWEBPUSH command returns a subset of webpush registrations from the complete set of all registrations available to the client. Zero or more untagged WEBPUSH responses are returned, containing information to identified the registrations. The server MUST return the WEBPUSH response for the exact registration ID if the account has a registration with this ID. It MUST return all the account's registrations if the argument is a wildcard "*". Example: C: a1 LWEBPUSH "*" S: * WEBPUSH "a8282bf9-6102-4e1b-bb61-d26d0e532e65" \ "https://push.endpoint.tld/random1" S: * WEBPUSH "80a3b492-bc9c-46a9-91ab-5866b27073bb" \ "https://push.endpoint.tld/random2" S: * WEBPUSH "28626e4e-37d1-456c-a667-5258b5528508" \ "https://push.endpoint.tld/random3" S: a1 OK LWEBPUSH completed C: a2 LWEBPUSH "a8282bf9-6102-4e1b-bb61-d26d0e532e65" S: * WEBPUSH "a8282bf9-6102-4e1b-bb61-d26d0e532e65" \ "https://push.endpoint.tld/random1" S: a2 OK LWEBPUSH completed 5. Server Responses 5.1. VAPID Response The VAPID response occurs as a result of a GETVAPID command. It returns the server VAPID public key ([RFC8292]). This is a public key on the P-256 curve. It MUST be encoded in the uncompressed form [SEC_1] (section 2.3.3, replicated from X9.62), and base64url encoded as described in [RFC7515]. The server MAY use a different key pair for each account. Example: S: * VAPID "BOniQ9xHBPNY9gnQW4o-16vHqOb40pEIMifyUdFsxAgy\ zVkFMguxw0QrdbZcq8hRjN2zpeInRvKVPlkzABvuTnI" 5.2. WEBPUSH Response The WEBPUSH response occurs as a result of a LWEBPUSH command. It MAY be returned as a result of a WEBPUSH command too. It contains the registration ID and the push endpoint of the registration. Example: Gougeon Expires 28 July 2025 [Page 6] Internet-Draft The IMAP WEBPUSH extension January 2025 S: * WEBPUSH "a8282bf9-6102-4e1b-bb61-d26d0e532e65" \ "https://push.endpoint.tld/random1" 5.3. SYNC Response The SYNC response is sent with a push notification by the server when a response that should be pushed exceed the 3993 bytes limit. It is used to inform the client that it SHOULD send a command to retrieve the response. It contains the response name in question. For example, if a server has a lot of flags, and the list exceed the limit, the server sends a SYNC for FLAGS. Example: S: * SYNC FLAGS 6. Push notifications Once an account has one or more push registration (registered with WEBPUSH command), the server sends a push message for each registration every time a change is recorded. This can be a change for the account (for example when a new permanent FLAG is added) or for the subscribed mailboxes (new mail, deletions, flag changes). The notification is encrypted following [RFC8291] specifications, send following [RFC8030] and authorized with [RFC8292]. 6.1. Content The server can send EXISTS, EXPUNGE, FETCH, and other responses at any time. Every response relative to a mailbox MUST be preceded by the mailbox name. The server MAY send multiple responses in a single push notification. As stated in RFC8291, the cleartext content of push notifications MUST NOT be longer than 3993 bytes. If the server wants to inform the client about a response longer than that, it MAY send a SYNC message. If the server sends a FETCH response, it MUST include a UID FETCH item. Every EXISTS response MUST be followed by a FETCH response. The FETCH response SHOULD contain the UID, the ENVELOPE, and the BINARY if it fits in the message length limits, or SHOULD contain the UID and the ENVELOPE, if it fits in the limits. So, when a new mail comes in, the server sends: * EXISTS Gougeon Expires 28 July 2025 [Page 7] Internet-Draft The IMAP WEBPUSH extension January 2025 * and FETCH (UID ENVELOPE BINARY) * or FETCH (UID ENVELOPE) * or FETCH (UID) Example of a push notification containing multiple responses for the "INBOX" mailbox:: INBOX 2 FETCH (UID 2 FLAGS (\Deleted \Seen)) INBOX 2 EXPUNGE Example of a push notification when a new mail arrives in the "New messages" mailbox: "New Messages" 2 EXISTS "New Messages" 2 FETCH (UID 3 ENVELOPE \ ("Mon, 7 Feb 1994 21:52:25 -0800 (PST)" \ "afternoon meeting" \ (("Fred Foobar" NIL "foobar" "Blurdybloop.example")) \ (("Fred Foobar" NIL "foobar" "Blurdybloop.example")) \ (("Fred Foobar" NIL "foobar" "Blurdybloop.example")) \ ((NIL NIL "mooch" "owatagu.siam.edu.example")) \ NIL NIL NIL "")) Example of a push notification to inform about a response longer than 3993 bytes: SYNC FLAGS 6.2. Push server response When the push server returns a 429 Too many requests, it should have send a Retry-After headers [RFC9110] to indicate how long the server has to wait before sending another request. If this header is present, the server MUST follow the period requested. If this header is not present, the mail server SHOULD wait 5 minutes before sending another request to this endpoint. When the push server returns another 4XX status code, the mail server MUST removes the registration. When the push server returns a 5XX status code, the mail server SHOULD wait 5 minutes before sending another request to the endpoint. Gougeon Expires 28 July 2025 [Page 8] Internet-Draft The IMAP WEBPUSH extension January 2025 7. Security Considerations The privacy and security considerations of [RFC8030] [RFC8291] and [RFC8292] all apply to the use of this extension. 8. IANA Considerations This document has no IANA actions. 9. References 9.1. Normative References [RFC8030] Thomson, M., Damaggio, E., and B. Raymor, Ed., "Generic Event Delivery Using HTTP Push", RFC 8030, DOI 10.17487/RFC8030, December 2016, . [RFC8292] Thomson, M. and P. Beverloo, "Voluntary Application Server Identification (VAPID) for Web Push", RFC 8292, DOI 10.17487/RFC8292, November 2017, . [RFC8291] Thomson, M., "Message Encryption for Web Push", RFC 8291, DOI 10.17487/RFC8291, November 2017, . [RFC9051] Melnikov, A., Ed. and B. Leiba, Ed., "Internet Message Access Protocol (IMAP) - Version 4rev2", RFC 9051, DOI 10.17487/RFC9051, August 2021, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022, . [SEC_1] "SEC 1: Elliptic Curve Cryptography", n.d., . [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015, . Gougeon Expires 28 July 2025 [Page 9] Internet-Draft The IMAP WEBPUSH extension January 2025 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . 9.2. Informative References [RFC2177] Leiba, B., "IMAP4 IDLE command", RFC 2177, DOI 10.17487/RFC2177, June 1997, . [RFC8620] Jenkins, N. and C. Newman, "The JSON Meta Application Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July 2019, . [RFC5465] Gulbrandsen, A., King, C., and A. Melnikov, "The IMAP NOTIFY Extension", RFC 5465, DOI 10.17487/RFC5465, February 2009, . Author's Address Simon Gougeon Email: ietf@sgougeon.fr Gougeon Expires 28 July 2025 [Page 10]