Don't know where it "does" this line, if it is a notice or snotice, you might use something like:
Code:
on *:snotice:*: {
  if (Authentication phrase isin $1-) { var %pass = $gettok($1-,-1,32) }
}
(assuming it's a server notice)

or
Code:
on *opperserv:notice:*:*: {
  var %reg = /.+Authentication phrase \(method=.+, para=.+\) is: .+/s
  if ($regex($1-,%reg)) { var %pass = $gettok($1-,-1,32) }
}
(assuming its a "regular" notice sent to you by opperserv)