def check_access_token(self, openid=None, access_token=None):
        """检查 access_token 有效性

        :param openid: 可选，微信 openid，默认获取当前授权用户信息
        :param access_token: 可选，access_token，默认使用当前授权用户的 access_token
        :return: 有效返回 True，否则 False
        """
        openid = openid or self.open_id
        access_token = access_token or self.access_token
        res = self._get(
            'sns/auth',
            params={
                'access_token': access_token,
                'openid': openid
            }
        )
        if res['errcode'] == 0:
            return True
        return False