https://mp.weixin.qq.com/debug/cgi-bin/sandboxinfo?action=showinfo&t=sandbox/index

<?php
/**
  * wechat php test
  */
//define your token
define("TOKEN", "abc123456");
$wechatObj = new wechatCallbackapiTest();
$wechatObj->valid();
class wechatCallbackapiTest
{
    public function valid()
    {
        $echoStr = $_GET["echostr"];
        //valid signature , option
        if($this->checkSignature()){
            echo $echoStr;
            exit;
        }
    }

    public function responseMsg()
    {
        //get post data, May be due to the different environments
        $postStr = $GLOBALS["HTTP_RAW_POST_DATA"];
        //extract post data
        if (!empty($postStr)){
                
              $postObj = simplexml_load_string($postStr, 'SimpleXMLElement', LIBXML_NOCDATA);
                $fromUsername = $postObj->FromUserName;
                $toUsername = $postObj->ToUserName;
                $keyword = trim($postObj->Content);
                $time = time();
                $textTpl = "<xml>
                <ToUserName><![CDATA[%s]]></ToUserName>
                <FromUserName><![CDATA[%s]]></FromUserName>
                <CreateTime>%s</CreateTime>
                <MsgType><![CDATA[%s]]></MsgType>
                <Content><![CDATA[%s]]></Content>
                <FuncFlag>0</FuncFlag>
                </xml>";             
                if(!empty( $keyword ))
                {
                    $msgType = "text";
                    $contentStr = "Welcome to wechat world!";
                    $resultStr = sprintf($textTpl, $fromUsername, $toUsername, $time, $msgType, $contentStr);
                    echo $resultStr;
                }else{
                    echo "Input something...";
                }
        }else {
        echo "";
        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;
        }
    }
}
?>

静默获取openid

<?php
    header("Content-type:text/html;charset=utf-8");
    //微信公众平台后台获取
    $appid='wxcd660206dc6b5e93';
    $secret='2fd906c63b63f0ce9390876675a0ff4a';
    //回调地址
    $redirect_uri='https://www.xiaoguan.net/2018/getOpenId/index.php';
    //获取成功后跳转地址
    $callback = 'https://www.xiaoguan.net/2018/getOpenId/index.php';
    //获取token和openid
    $code = $_GET['code'];
    if($code){
        $url = 'https://api.weixin.qq.com/sns/oauth2/access_token?appid='.$appid.'&secret='.$secret.'&code='.$code.'&grant_type=authorization_code';
        $html = file_get_contents($url);
        $json = json_decode($html);
        var_dump($json);die();
    }else{
        header('Location: https://open.weixin.qq.com/connect/oauth2/authorize?appid='.$appid.'&redirect_uri='.$redirect_uri.'&response_type=code&scope=snsapi_base&state=ssaweqeqew#wechat_redirect');
    }
?>