+If the channel has the +C (channel public key authentication,
+see /HELP CMODE) mode set then the user joining the channel must
+provide the -auth option to JOIN command. This option will attempt to
+authenticate the user on the channel. If the user's public key has
+not been added to the channel's public key list, user will not be
+able to join. User may optionally provide the <pubkeyfile>,
+<privkeyfile> and <privkey passphrase> to authenticate with some other
+key pair than with the user's default key pair.
+