WeChat パブリック プラットフォーム、PHP 開発に関する簡単な質問

<?php/**  * wechat php test  *///define your tokendefine("TOKEN", "weixin");$wechatObj = new wechatCallbackapiTest();$wechatObj->valid();class wechatCallbackapiTest{	public function valid()    {        $echoStr = $_GET["echostr"];        //valid signature , option        if($this->checkSignature()){        	echo $echoStr;        	exit;        }    }			private function checkSignature()	{        $signature = $_GET["signature"];        $timestamp = $_GET["timestamp"];        $nonce = $_GET["nonce"];	        				$token = TOKEN;		$tmpArr = array($token, $timestamp, $nonce);		sort($tmpArr);		$tmpStr = implode( $tmpArr );		$tmpStr = sha1( $tmpStr );				if( $tmpStr == $signature ){			return true;		}else{			return false;		}	}}?>