def _make_common_signature(self):
        """生成通用签名, 一般情况下，您不需要调用该方法 文档详见 http://docs.rongcloud.cn/server.html#_API_调用签名规则
        :return: {'app-key':'xxx','nonce':'xxx','timestamp':'xxx','signature':'xxx'}
        """
        nonce = str(random.random())
        timestamp = str(int(time.time()) * 1000)
        signature = hashlib.sha1((self._app_secret + nonce + timestamp).encode(
            'utf-8')).hexdigest()

        return {
            "rc-app-key": self._app_key,
            "rc-nonce": nonce,
            "rc-timestamp": timestamp,
            "rc-signature": signature
        }