SMTP Service Extension for Authentication (RFC2554)
Original Publication Date: 1999-Mar-01
Included in the Prior Art Database: 2019-Feb-11
Internet Society Requests For Comment (RFCs)
This document defines an SMTP service extension [ESMTP] whereby an SMTP client may indicate an authentication mechanism to the server, perform an authentication protocol exchange, and optionally negotiate a security layer for subsequent protocol interactions. [STANDARDS-TRACK]
Network Working Group J. Myers Request for Comments: 2554 Netscape Communications Category: Standards Track March 1999
SMTP Service Extension for Authentication
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document defines an SMTP service extension [ESMTP] whereby an SMTP client may indicate an authentication mechanism to the server, perform an authentication protocol exchange, and optionally negotiate a security layer for subsequent protocol interactions. This extension is a profile of the Simple Authentication and Security Layer [SASL].
2. Conventions Used in this Document
In examples, "C:" and "S:" indicate lines sent by the client and server respectively.
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in this document are to be interpreted as defined in "Key words for use in RFCs to Indicate Requirement Levels" [KEYWORDS].
3. The Authentication service extension
(1) the name of the SMTP service extension is "Authentication"
(2) the EHLO keyword value associated with this extension is "AUTH"
Myers Standards Track [Page 1]
RFC 2554 SMTP Authentication March 1999
(3) The AUTH EHLO keyword contains as a parameter a space separated list of the names of supported SASL mechanisms.
(4) a new SMTP verb "AUTH" is defined
(5) an optional parameter using the keyword "AUTH" is added to the MAIL FROM command, and extends the maximum line length of the MAIL FROM command by 500 characters.
(6) this extension is appropriate for the submission protocol [SUBMIT].
4. The AUTH command
AUTH mechanism [initial-response]
Arguments: a string identifying a SASL authentication mechanism. an optional base64-encoded response
Restrictions: After an AUTH command has successfully completed, no more AUTH commands may be issued in the same session. After a successful AUTH command completes, a server MUST reject any further AUTH commands with a 503 reply.
The AUTH command is not permitted during a mail transaction.
Discussion: The AUTH command indicates an authentication mechanism to the server. If the server supports the requested authentication mechanism, it performs an authentication protocol exchange to authenticate and identify the user. Optionally, it also negotiates a security layer for subsequent protocol interactions. If the requested authentication mechanism is not supported, the server rejects the AUTH command with a 504 reply.
The authentication protocol exchange consists of a series of server challenges and client answers that are specific to the authentication mechanism. A server challenge, otherwise known as a ready response, is a 3...