Network Working Group A. Melnikov
Internet-Draft Isode Ltd
Intended status: Standards Track 14 February 2025
Expires: 18 August 2025
IMAP REMEMBERME extension for quick reauthentication token generation
draft-melnikov-imap-rememberme-00
Abstract
This document specifies an IMAP extension for generating quick
reauthentication tokens that allow clients to re-login without user
interaction, once authentication using a strong SASL mechanism is
completed.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. REMEMBERME command . . . . . . . . . . . . . . . . . . . . . 3
4. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
This document specifies an IMAP [RFC9051] extension which is a
protocol specific extension to Simple Authentication and Security
Layer (SASL) [RFC4422] framework for generation of proof-of-posession
reauthentication tokens. Such tokens can be used for subsequent 1
roundtrip reauthentication using SASL mechanisms such as REMEMBERME
and HT-*.
The typical sequence of events is going to be like this:
1. Client establishes IMAP connection protected by TLS on Connection
1.
2. On Connection 1 the client authenticates using a strong SASL
mechanism, which might be CPU intensive, and most likely requires
user interaction, e.g., SCRAM with 2FA extension, PASSKEY.
3. On Connection 1 the client requests reauthentication token using
REMEMBERME command.
4. <Connection gets interrupted or closed due to inactivity>
5. Client establishes another IMAP connection protected by TLS on
Connection N. The client then uses a previous issues quick
reauthentication token with one of 1 round trip SASL mechanisms
such as REMEMBERME and HT-*. The same token is reusable on other
IMAP connections until it is replaced or revoked.
IMAP servers advertise support for this extension by returning one or
more TOKEN=<token-type> capabilities in the CAPABILITY response.
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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. REMEMBERME command
Arguments: Token type
Responses: REQUIRED TOKEN response code
Result: OK - new token successfully issued
NO - authentication mechanism too week, unrecognized
token type
BAD - command unknown or arguments invalid,
invalid state
This command is only allowed in authenticated state.
Upon receipt of REMEMBERME command the IMAP server checks that the
specified token type is recognized and supported. If it is, it
generates a new token of the requested type and returns it in the
TOKEN response code in the tagged OK response.
S: * OK ACME IMAP Server v1.23 is ready
C: 22 CAPABILITY
S: * CAPABILITY IMAP4rev1 IMAP4rev2 STARTTLS AUTH=PASSKEY AUTH=REMEMBERME AUTH=SCRAM-SHA-256 TOKEN=JWT TOKEN=RANDOM
S: 22 CAPABILITY completed
C: 23 STARTTLS
S: 23 OK Completed
C: 24 AUTHENTICATE ...
<SASL exchange>
S: 24 OK Completed
C: 25 REMEMBERME JWT
S: 26 OK [TOKEN <base64-encoded token>] Completed
4. Formal Syntax
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capability =/ "TOKEN=" token-type
;; <capability> from [RFC3501]
token-type = atom
;; SHOULD be registered with IANA
resp-text-code =/ "TOKEN" SP base64-token
base64-token = base64
5. IANA Considerations
TBD. Regeister the IMAP capabilities and create a separate registry
of token types.
6. Security Considerations
TBD.
7. Normative References
[ABNF] Crocker, D., Ed. and P. Overell, Ed., "Augmented BNF for
Syntax Specifications: ABNF", RFC 5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[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>.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
<https://www.rfc-editor.org/info/rfc3501>.
[RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)", RFC 4422,
DOI 10.17487/RFC4422, June 2006,
<https://www.rfc-editor.org/info/rfc4422>.
[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>.
[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/info/rfc9051>.
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Author's Address
Alexey Melnikov
Isode Ltd
14 Castle Mews
Hampton
TW12 2NP
United Kingdom
Email: alexey.melnikov@isode.com
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