@abstractmethod<EOL><INDENT>def has_role(self, role_s):<DEDENT>
pass<EOL>
Determines whether a Subject is a member of the Role(s) requested

:param role_s: 1..N role identifiers (strings)
:type role_s:  Set of Strings

:returns: a set of tuple(s), each containing the Role identifier
          requested and a Boolean indicating whether the subject is
          a member of that Role
          - the tuple format is: (role, Boolean)