1，公众平台配置回调域名，则通过微信访问域名会先跳转到微信 oauth2 接口，访问成功微信会返回一个用户code给回调地址

请求地址：$url ="https://open.weixin.qq.com/connect/oauth2/authorize?appid=".$appid."&redirect_uri=".$redirect_uri."&response_type=code&scope=snsapi_userinfo&state=STATE#wechat_redirect";
2，根据返回的code获取access_token和用户唯一标识openid

请求地址：$url = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=".$appid."&secret=".$secret."&code=".$code."&grant_type=authorization_code";

3，通过获取到的access_token 和 openid 即可获取到用户信息

请求地址：$urltoc = "https://api.weixin.qq.com/sns/userinfo?access_token=".$access_token."&openid=".$getopenid."&lang=zh_CN";

<?php
namespace app\home\controller;
use think\Controller;
use think\Db;
use think\Session;
use think\Request;
 
class Index extends Controller{
     public function index(){
        // 访问域名会优先执行index方法，用以获取到code
        $dbres = Db::name("setup")->find();
        $appid = $dbres['appid'];
        $redirect_uri = urlencode($dbres['back_url']);
        $url ="https://open.weixin.qq.com/connect/oauth2/authorize?appid=".$appid."&redirect_uri=".$redirect_uri."&response_type=code&scope=snsapi_userinfo&state=STATE#wechat_redirect";
        header("Location:".$url);exit;
    }
 
    public function http_curl($url,$type='get',$res='json',$arr=''){
        //1.初始化curl
        $ch = curl_init();
        //2.设置curl的参数
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false); //不验证证书
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false); //不验证证书
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        if ($type == 'post') {
            curl_setopt($ch, CURLOPT_POST, 1);
            curl_setopt($ch, CURLOPT_POSTFIELDS, $arr);
        }
        //3.采集
        $output = curl_exec($ch);
        //4.关闭
        curl_close($ch);
        if ($res == 'json') {
            return json_decode($output,true);
        }
    }
 
    public function getUserOpentId(){
        //回调地址会传回一个code，则我们根据code去获取openid和授权获取到的access_token
        $code = $_GET['code'];
        $dbres = Db::name("setup")->find();
        $appid = $dbres['appid'];
        $secret = $dbres['appsecret'];
 
        $url = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=".$appid."&secret=".$secret."&code=".$code."&grant_type=authorization_code";
 
        $res = $this->http_curl($url);
        $access_token = $res['access_token'];
 
        $getopenid = $res['openid'];
        //获取用户授权信息
        $urltoc = "https://api.weixin.qq.com/sns/userinfo?access_token=".$access_token."&openid=".$getopenid."&lang=zh_CN";
        $resinfos = $this->http_curl($urltoc);
        $openid = $resinfos['openid'];
        $check_member = Db::name("member")->where('openid',$openid)->find();
        if(empty($check_member)){
            //首次进入，则获取用户信息，插入数据库
            $resinfo['openid'] = $openid;
            $insert_data = [
                'openid' => $openid,
                'create_time' => time()
            ];
            Db::name("member")->insert($insert_data);
            $userId = Db::name('member')->getLastInsID();
            Session::set('wx_member_info', $resinfo);
            $this->redirect('home/index/index_html');
        }else{
            //说明是已经是公众号成员，则调用用户信息存到session即可
            $wx_member_info = Db::name('member')->where("openid",$openid)->find();
            Session::set('wx_member_info', $wx_member_info);
            $this->redirect('home/index/index_html');
        }
    }
 
    public function index_html(){
        if(!Session::has("wx_member_info")){
            action("home/index/index");
        }else{
            return $this->fetch('index');
        }
    }
 
}