Authenticate the client using an SASL[4] authentication mechanism.
Syntax:
AUTH <name> <seq> [:<parameter>]
<name> The name of the SASL mechanism to use for authentication.
<seq> The sequence is a value of 'I' or 'S'. The 'I' value is specified for the initial AUTH message and the 'S' value is specified for all subsequent AUTH messages. If the client specifies '*' for the sequence, the server will abort the authentication sequence and return IRCERR_AUTHENTICATIONFAILED.
<parameter> This is optional data sent as an argument with the AUTH messages. The content depends on the authentication mechanism being used. All content must use standard escaping formats (e.g. \r for carriage return) to comply with IRC message format restrictions.
               ERR_NEEDMOREPARAMS
               IRCERR_ALREADYAUTHENTICATED
               IRCERR_ALREADYREGISTERED
               IRCERR_AUTHENTICATIONFAILED
               IRCERR_AUTHENTICATIONSUSPENDED
               IRCERR_BADCOMMAND
               IRCERR_UNKNOWNPACKAGE
            
If the server is known to support IRCX with specific SASL mechanism(s), then the first message from an IRCX-compliant client must be the AUTH command (if authentication is to be used), before the USER and NICK commands. Use MODE ISIRCX to determine if the server supports IRCX.