RFC 2554 (rfc2554) - Page 2 of 11
SMTP Service Extension for Authentication
Alternative Format: Original Text Document
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 334 reply with the text part
containing a BASE64 encoded string. The client answer consists
of a line containing a BASE64 encoded string. If the client
wishes to cancel an authentication exchange, it issues a line
with a single "*". If the server receives such an answer, it
MUST reject the AUTH command by sending a 501 reply.
Myers Standards Track