docs: 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
          }