Value of specified method. For command and exec authorization types, set of method values are different and are as follows: * command: tacacs(1), radius(2), none(4); * exec: tacacs(1), radius(2), local(3), none(4). Undefined(0) value is being used for displaying empty method. Setting this object to undefined will clear configured method from the list. A list of authentication methods may not be modified once associated to an access line.