private function checkSignature()
{
        // 将token、timestamp、nonce三个参数进行字典序排序
        $signature = $_GET["signature"];
        $timestamp = $_GET["timestamp"];
        $nonce = $_GET["nonce"];    
                
    $token = TOKEN;
    $tmpArr = array($token, $timestamp, $nonce);
    sort($tmpArr, SORT_STRING);

        //将三个参数字符串拼接成一个字符串进行sha1加密
    $tmpStr = implode( $tmpArr );
    $tmpStr = sha1( $tmpStr );
    
        //开发者获得加密后的字符串可与signature对比，标识该请求来源于微信
    if( $tmpStr == $signature ){
        return true;
    }else{
        return false;
    }
}