public function valid() {
        if (isset($_GET["echostr"])) {
            $echoStr = $_GET["echostr"];
            //valid signature , option
            if (!$this->token) {
                throw new Exception(‘token is not defined!‘);
            }
            $signature = $_GET["signature"];
            $timestamp = $_GET["timestamp"];
            $nonce = $_GET["nonce"];
            $tmpArr = array($this->token, $timestamp, $nonce);
            // use SORT_STRING rule
            sort($tmpArr, SORT_STRING);
            $tmpStr = implode($tmpArr);
            $tmpStr = sha1($tmpStr);
            if ($tmpStr == $signature) {
                ob_clean();
                echo $_GET[‘echostr‘];
            } else {
                echo ‘xx‘;
            }
        } else {
            $this->responseMsg();
        }
    }