@abc.abstractmethod<EOL><INDENT>def get_authorization_session(self):<DEDENT>
return<EOL>
Gets an ``AuthorizationSession`` which is responsible for performing authorization checks.

        :return: an authorization session for this service
        :rtype: ``osid.authorization.AuthorizationSession``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``Unimplemented`` -- ``supports_authorization()`` is ``false``

        *compliance: optional -- This method must be implemented if
        ``supports_authorization()`` is ``true``.*