docs: def fetch_access_token(self, code):
          """获取 access_token
  
          :param code: 授权完成跳转回来后 URL 中的 code 参数
          :return: JSON 数据包
          """
          res = self._get(
              'sns/oauth2/access_token',
              params={
                  'appid': self.app_id,
                  'secret': self.secret,
                  'code': code,
                  'grant_type': 'authorization_code'
              }
          )
          self.access_token = res['access_token']
          self.open_id = res['openid']
          self.refresh_token = res['refresh_token']
          self.expires_in = res['expires_in']
          return res