def get_authentication_acquisition_session(self):
raise Unimplemented()<EOL>
Gets an ``AuthenticationAcquisitionSession`` which is responsible for acquiring authentication credentials on behalf of a service client.

        return:
                (osid.authentication.process.AuthenticationAcquisitionSe
                ssion) - an acquisition session for this service
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented -
                ``supports_authentication_acquisition()`` is ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_acquisition()`` is ``true``.*