The login method. The allowed options are:
null : Default
"nickServMsg" : NickServ (/MSG NickServ + password)
"nickServ" : NickServ (/NICKSERV + password)
"challengeAuth" : Challenge Auth (username + password)
"sasl" : SASL (username + password)
"serverPassword" : Server password (/PASS password)
"saslExternal" : SASL EXTERNAL (cert)
"customCommands" : Use "commands" field for auth. For example
commands = [ "/msg NickServ IDENTIFY my_password" ]