Authenticate the connection, so that privileged commands can
be executed. Username and password must be authenticated by one of the
Monitor's AuthBy clauses, or by the hardwired Username and Password (if
present).
Password may be either a plaintext password or a CHAP
response to a previously issued CHALLENGE command.
LOGIN mikem fred
LOGGEDIN
or
CHALLENGE
CHALLENGE 5b0e00b1a379ae225634946268cc0144
LOGIN mikem {chap}4bda435ca72249c0e9fe05d32775eb6e98
LOGGEDIN