def has_role(self, identifiers, role_s):
return self.authorizer.has_role(identifiers, role_s)<EOL>
:type identifiers: SimpleIdentifierCollection

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

:returns: a set of tuple(s), containing the role and a Boolean
          indicating whether the user is a member of the Role