code: def signOp(self,
                 op: Dict,
                 identifier: Identifier=None) -> Request:
          
          request = Request(operation=op,
                            protocolVersion=CURRENT_PROTOCOL_VERSION)
          return self.signRequest(request, identifier)
docs: Signs the message if a signer is configured
  
          :param identifier: signing identifier; if not supplied the default for
              the wallet is used.
          :param op: Operation to be signed
          :return: a signed Request object