Adds the following defaults to the payload:
          __rev, __user, __a, ttstamp, fb_dtsg, __req

def _generatePayload(self, query):
        """Adds the following defaults to the payload:
          __rev, __user, __a, ttstamp, fb_dtsg, __req
        """
        payload = self._payload_default.copy()
        if query:
            payload.update(query)
        payload["__req"] = str_base(self._req_counter, 36)
        payload["seq"] = self._seq
        self._req_counter += 1
        return payload