PASS

The PASS command is used to set a connection password, or to identify ownership of a nickname account registration during a challenge.

Connection Password / Nickname Authentication

Usage: PASS <password>
<password> The connection password or nickname account password.

The PASS command must be sent before any other commands during initial connection for server authentication. It can also be sent after the connection process to prove ownership of a registered nickname during a challenge.

(See section 3.1.1 of RFC2812)