Defines the method of authentication. Either individual
users, or the <default> entry can accomodate various methods
of authentication. The 'always reject' will prohibit the
corresponding user (specific or default) from ever being
authenticated. The use of 'always accept' will always
authenticate the corresponding user, regardless of which
password was used. 'Internal Authentication' performs
password validation for a specific user. 'Radius Authentication'
attempts to use a configured Radius server to determine whether
or not a user is authenticated.