code: def parse_authn_request(self, enc_request, binding=BINDING_HTTP_REDIRECT):
          
  
          return self._parse_request(enc_request, AuthnRequest,
                                     "single_sign_on_service", binding)
docs: Parse a Authentication Request
  
          :param enc_request: The request in its transport format
          :param binding: Which binding that was used to transport the message
              to this entity.
          :return: A request instance