微信公众平台的消息推送 PHP 的示例代码，版本最多兼容到7，php 8以上不支持，主要是加解密的函数更新了，自己封装了个适应 php 8 的示例 demo，当前 demo 里我使用的是 laravel 框架，涉及到了随机数生成的助手函数 Str::random

<?php

namespace App\Services;

use App\Exceptions\WechatException;
use Illuminate\Support\Str;
use SimpleXMLElement;

class WechatNotifyService
{
    private $token;
    private $appId;
    private $encodingAesKey;
    private $aesKey;
    private $iv;

    public function __construct()
    {
        $this->token = config('wechat.token');
        $this->appId = config('wechat.app_id');
        $this->encodingAesKey = config('wechat.aes_key');
        $this->aesKey = base64_decode($this->encodingAesKey . '=');
        $this->iv = substr($this->aesKey, 0, 16);
    }

    /**
     * 验证签名
     *
     * @param $signature
     * @param $timestamp
     * @param $nonce
     * @return bool
     */
    public function checkSignature($signature, $timestamp, $nonce)
    {
        $sign = $this->genSign($timestamp, $nonce);

        if ($sign == $signature) {
            return true;
        } else {
            return false;
        }
    }

    /**
     * 生成签名
     *
     * @return string
     */
    public function genSign($timestamp, $nonce)
    {
        $tmpArr = array($this->token, $timestamp, $nonce);
        sort($tmpArr, SORT_STRING);
        $tmpStr = implode($tmpArr);
        return sha1($tmpStr);
    }

    /**
     * 解密数据
     *
     * @return array
     * @throws WechatException
     */
    public function decrypt($postData, $timestamp, $nonce, $msgSignature)
    {
        $array = array($postData, $this->token, $timestamp, $nonce);
        sort($array, SORT_STRING);
        $str = implode($array);
        $sign = sha1($str);

        if ($sign != $msgSignature) {
            throw new WechatException('加密数据签名验证失败');
        }

        try {
            $base64Decode = base64_decode($postData);
            $data = openssl_decrypt($base64Decode, 'aes-256-cbc', $this->aesKey, OPENSSL_RAW_DATA, $this->iv);
            $filterHeader = substr($data, 20);
            $content = preg_replace('/' . $this->appId . '/', '', $filterHeader);
            return json_decode($content, true);
        } catch (\Throwable $e) {
            throw new WechatException('解密数据失败'. $e->getMessage());
        }
    }

    /**
     * 加密数据
     *
     * @return string
     */
    public function encrypt($data)
    {
        $random = Str::random(16);
        $len = pack('N', strlen($data));
        $content = $random . $len . $data . $this->appId;

        $result = openssl_encrypt($content, 'aes-256-cbc', $this->aesKey, OPENSSL_RAW_DATA, $this->iv);
        return base64_encode($result);
    }

    /**
     * 加密响应
     *
     * @param $timestamp
     * @param $nonce
     * @return string
     */
    public function response($timestamp, $nonce)
    {
        // 创建一个XML文档
        $xml = new SimpleXMLElement('<xml></xml>');

        $data = json_encode([
            'ToUserName' => '',
            'FromUserName' => '',
            'CreateTime' => time(),
            'MsgType' => '',
            'Content' => 'success'
        ]);

        $encrypt = $this->encrypt($data);
        $sign = $this->genSign($timestamp, $nonce);

        // 添加子元素
        $xml->addChild('Encrypt', $encrypt);
        $xml->addChild('MsgSignature', $sign);
        $xml->addChild('TimeStamp', $timestamp);
        $xml->addChild('Nonce', $nonce);

        return preg_replace('/<\?xml.*\?>/i', '', $xml->asXML());
    }
}