code: def _auth(self):
          
          codec = PbufCodec()
          username = self._client._credentials.username
          password = self._client._credentials.password
          if not password:
              password = ''
          msg = codec.encode_auth(username, password)
          resp_code, _ = self._non_connect_send_recv_msg(msg)
          if resp_code == riak.pb.messages.MSG_CODE_AUTH_RESP:
              return True
          else:
              return False
docs: Perform an authorization request against Riak
          returns True upon success, False otherwise
          Note: Riak will sleep for a short period of time upon a failed
                auth request/response to prevent denial of service attacks