返回当前用户所匹配的首个有效权限

async def verify_permissions(self, user_id, *permissions):
        """ 返回当前用户所匹配的首个有效权限 """

        prefix = f"{self._prefix_perm}/{user_id}/"

        perm_names = [str(p) for p in permissions]
        
        checkings = [KV.get.txn(prefix + p) for p in perm_names]
        success, responses = await self._client.txn(compare=[], success=checkings)
        if not success:
            errmsg = f"无法读取用户({user_id})的权限信息"
            raise Unprocessable(errmsg)

        for i, item  in enumerate(responses):
            if item[0] is not None:
                return permissions[0]
                
        return None