EXTRA A. Gulbrandsen
Internet-Draft ICANN
Intended status: Standards Track B. Gondwana
Expires: 27 January 2024 Fastmail
26 July 2023
The JMAPACCESS Extension for IMAP
draft-ietf-extra-jmapaccess-04
Abstract
This document defines an IMAP extension to let clients know that the
messages in this IMAP server are also available via JMAP, and how.
It is intended for clients that want to migrate gradually to JMAP.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. Details . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. The JMAPACCESS and DEBUGGING Response Codes . . . . . . . . . 3
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
A few IMAP client maintainers have asked for ways to use features
that are available in JMAP without having to drop their expensively
tested IMAP code.
This document provides a server with a way to declare that the
messages in its mailstore are also available via JMAP. For
simplicity, only a complete equivalence is supported (the same set of
messages are available via both IMAP and JMAP).
2. Requirements Language
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. Details
By advertising the JMAPACCESS capability, the server asserts that if
a mailbox or message has a particular object ID when accessed via
either IMAP or JMAP (see [RFC3501], [RFC9051] and [RFC8620]), then
the same mailbox or message is accessible via the other protocol, and
it has the same ID.
The server MUST also advertise the OBJECTID extension, defined by
[RFC8474]. The JMAP session resource that allows access to the same
messages is called "the JMAP server" below.
This specification does not affect message lifetime: If a client
accesses a message via IMAP and half a second later via JMAP, then
the message may have been deleted.
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When the server processes the client's LOGIN/AUTHENTICATE command and
enters Authenticated state, the server considers the way the client
authenticated. If the IMAP server can infer from the client's
authentication process that its credentials suffice to authenticate
via JMAP, then the server MUST also send a JMAPACCESS response code
containing a link to the JMAP server.
If the credentials might not succeed with the JMAP server, then the
server SHOULD send an untagged OK response with a DEBUGGING response
code with a message to help client developers understand why this
authentication would not work with the JMAP server.
Servers are encouraged to report the same message flags and other
data via both protocols, as far as possible.
This specification does not require mailboxes to have the same name
in IMAP and JMAP, even if they share mailbox ID. However, the JMAP
specification regulates that, in the text about the name and role
properties in [RFC8620] section 2.
Note that all JMAP servers support internationalized email addresses
(see [RFC6530]). If this IMAP server does not, or the IMAP client
does not issue ENABLE UTF8=ACCEPT (see [RFC6855]), then there is a
possibility that the client receives accurate address fields via JMAP
and downgraded fields via IMAP (see (see [RFC6857] and [RFC6858] for
examples).
4. The JMAPACCESS and DEBUGGING Response Codes
The JMAPACCESS response code is followed by a single link to a JMAP
session resource. The server/mailstore at that location is
referenced as "the JMAP server" in this document.
The DEBUGGING response code asserts that when used with a status
response, the client may safely forward the string argument to the
client maintainers. The argument MUST NOT contain any message
contents or other personal information.
The formal syntax in [RFC9051] is extended thus:
resp-code-jmapaccess = "JMAPACCESS" SP (atom / quoted)
resp-code-debugging = "DEBUGGING" SP (atom / quoted)
resp-text-code =/ resp-code-jmapaccess / resp-code-debugging
The syntax in [RFC3501] is extended similarly (this extension may be
used with IMAP4rev1 as well as IMAP4rev2).
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5. Examples
Lines sent by the client are preceded by C:, lines sent by the server
by S:. Each example starts with the IMAP banner issued when the
client connects, and generally contains only those capabilities
required by the example itself, omitting even required capabilities
such as OBJECTID, JMAPACCESS and STARTTLS.
Example 1. A client connects, sees that SASL OAUTH is available, and
authenticates in that way.
S: * OK [CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR] example1
C: 1 AUTHENTICATE OAUTHBEARER bixhPXVzZ...QEB
The server processes the command successfully. Since it knows that
the client used Oauth, and that it and its JMAP alter ego use the
same Oauth backend subsystem, the server infers that the (next)
access token is just a usable via JMAP as via IMAP. It issues a
JMAPACCESS response code in its reply:
S: 1 OK [JMAPACCESS https://example.com/jmap] done
SASL OAUTH is specified by [RFC7628], and the argument in this
example is abbreviated from the more realistic length used in
RFC7628.
Example 2. A client connects, sees no SASL method it recognises, and
issues a LOGIN command.
S: * OK [CAPABILITY IMAP4rev2] example2
C: 2 LOGIN "arnt" "trondheim"
The server sees that the password is accepted, knows that it and its
JMAP alter ego the same password database, and issues a JMAPACCESS
response code:
S: * OK [JMAPACCESS "https://example.com/.s/[jmap]"] For JMAP access
S: 2 OK done
The URL is quoted since the ] character must be quoted. The URL uses
the same quoting rules as most other IMAP strings.
Example 3. A client connects, sees no SASL method it recognises, and
issues a LOGIN command with a correct password.
S: * OK [CAPABILITY IMAP4rev1 IMAP4rev2] example3
C: 3 LOGIN "arnt" "trondheim"
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The server operator has decided to disable password use with JMAP,
but allow it for a while with IMAP to cater to older clients. The
server issues a DEBUGGING response code in its reply:
S: 3 OK [DEBUGGING "Cleartext passwords are being disabled"] done
The message is quoted since it contains spaces. The message uses the
same quoting rules as most other IMAP strings.
Example 4. A client connects, sees no SASL method it recognises, and
issues a LOGIN command. Its password is incorrect.
S: * OK [CAPABILITY IMAP4rev2 AUTH=GSS] example4
C: 4 LOGIN "arnt" "oslo"
The server does not enter Authenticated state, so nothing requires it
to issue either JMAPACCESS or DEBUGGING. It replies curtly:
S: 4 NO done
6. IANA Considerations
The IANA is requested to add the JMAPACCESS and DEBUGGING response
codes to the IMAP Response Codes registry.
7. Security Considerations
DEBUGGING reveals to clients why they cannot auhenticate to the JMAP
server. One normally does not want to reveal anything about why a
client cannot authenticate, for fear of giving useful information to
an intruder.
However, in this case the client has already authenticated via IMAP.
By doing so the client already gained access to all of the same mail.
The authors believe that the debugging value of the response code far
outweighs its security concerns.
8. References
8.1. Normative References
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
<https://www.rfc-editor.org/rfc/rfc3501>.
[RFC8474] Gondwana, B., Ed., "IMAP Extension for Object
Identifiers", RFC 8474, DOI 10.17487/RFC8474, September
2018, <https://www.rfc-editor.org/rfc/rfc8474>.
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[RFC9051] Melnikov, A., Ed. and B. Leiba, Ed., "Internet Message
Access Protocol (IMAP) - Version 4rev2", RFC 9051,
DOI 10.17487/RFC9051, August 2021,
<https://www.rfc-editor.org/rfc/rfc9051>.
[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/rfc/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/rfc/rfc8174>.
8.2. Informative References
[RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", RFC 6530, DOI 10.17487/RFC6530,
February 2012, <https://www.rfc-editor.org/rfc/rfc6530>.
[RFC6855] Resnick, P., Ed., Newman, C., Ed., and S. Shen, Ed., "IMAP
Support for UTF-8", RFC 6855, DOI 10.17487/RFC6855, March
2013, <https://www.rfc-editor.org/rfc/rfc6855>.
[RFC6857] Fujiwara, K., "Post-Delivery Message Downgrading for
Internationalized Email Messages", RFC 6857,
DOI 10.17487/RFC6857, March 2013,
<https://www.rfc-editor.org/rfc/rfc6857>.
[RFC6858] Gulbrandsen, A., "Simplified POP and IMAP Downgrading for
Internationalized Email", RFC 6858, DOI 10.17487/RFC6858,
March 2013, <https://www.rfc-editor.org/rfc/rfc6858>.
[RFC7628] Mills, W., Showalter, T., and H. Tschofenig, "A Set of
Simple Authentication and Security Layer (SASL) Mechanisms
for OAuth", RFC 7628, DOI 10.17487/RFC7628, August 2015,
<https://www.rfc-editor.org/rfc/rfc7628>.
[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/rfc/rfc8620>.
Authors' Addresses
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Arnt Gulbrandsen
ICANN
6 Rond Point Schumann, Bd. 1
1040 Brussels
Belgium
Email: arnt@gulbrandsen.priv.no
URI: https://icann.org/ua
Bron Gondwana
Fastmail
Level 2, 114 William St.
Melbourne VIC 3000
Australia
Email: brong@fastmailteam.com
URI: https://fastmail.com
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