'Get me all services with a specified
entity ID and type, that supports the specified version of binding.
:param entity_id: The EntityId
:param typ: Type of service (idp, attribute_authority, ...)
:param service: which service that is sought for
:param binding: A binding identifier
:return: list of service descriptions.
Or if no binding was specified a list of 2-tuples (binding, srv)'

def service(self, entity_id, typ, service, binding=None):

    raise NotImplementedError
