微信浏览器里的code来源：

let redirect_uri = 'https://.../login'; //指定授权登录后跳转的页面，用于解析code,一般是登录页面
    let appid = this.$appid;//公众号id
//跳转微信授权页并获取code，然后他会通过redirect_rui来重新跳回你指定的页面
let url = 'https://open.weixin.qq.com/connect/oauth2/authorize?appid=' + appid + '&redirect_uri=' + link +
                    '&response_type=code&scope=snsapi_base&state=STATE#wechat_redirect'
                location.href = url;

login 回调页面

      _getParam(path, name) {
        var reg = new RegExp("(^|\\?|&)" + name + "=([^&]*)(\\s|&|$)", "i");
        if (reg.test(path)) {
          return unescape(RegExp.$2.replace(/\+/g, " "));
        }
        return '';
      },
checkIfWeixinLoginBack(){
         let thsUrl = location.href;//拿取当前url
        // console.log('thsUrl', thsUrl);
        let code = this._getParam(thsUrl, 'code');
        if(code.length>5) {
          let array_ = thsUrl.split('?');//将url截开
          let gobackToUsUrl = localStorage.getItem('wxLoginBeforeUrl');
          if(!gobackToUsUrl) {
            gobackToUsUrl = array_[0] +'/#/pages/home/index';
          }
          localStorage.removeItem('wxLoginBeforeUrl');

          // console.log('wxCode', code);
          // 提交code给php解析openid
          this.$api.wxCodeUpdateUser({code: code})
              .then(res =>{
                // console.log('res', res);
                // return;
                uni.hideLoading()
                //hash模式链接会有#
                //当链接带有#去请求code值，code会一直跟在链接后面
                //解决拿到code值后，每次跳转页面路径都会带有code值的问题
                window.location.href = gobackToUsUrl;
              })
              .catch(err =>{
                // console.log('resErr', err);
                // return;
                uni.hideLoading()
                //hash模式链接会有#
                //当链接带有#去请求code值，code会一直跟在链接后面
                //解决拿到code值后，每次跳转页面路径都会带有code值的问题
                window.location.href = gobackToUsUrl;
              })
        }


            },

appid和密钥获取方式：

php需要解析前端授权登录后提交的code

 //获取用户openid
    protected function _getOpenID($appid, $appsecret, $code)
    {
        $url = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=" . $appid . "&secret=" . $appsecret . "&code=" . $code . "&grant_type=authorization_code";
        $weixin = file_get_contents($url);//通过code换取网页授权access_token
        $jsondecode = json_decode($weixin); //对JSON格式的字符串进行编码
        $array = get_object_vars($jsondecode);//转换成数组

        if (isset($array["openid"])) {
            $openid = $array["openid"];//输出openid
        } else {
            $openid = 0;
        }
        return $openid;
    }


 $params = $this->request->post();

        if (!isset($params['code']) || empty($params['code'])) {
            $this->error('缺失参数code');
        }
        $myUid = $this->auth->id;
        //获取用户Openid
        $appid = Env::get('weixin.appId');
        $secret = Env::get('weixin.secret');
        // $appid = 'wx01eb21debee79a37';
        // $secret = 'add4d54b11f7a52b47ded252b4da0706';
        $openId = $this->_getOpenID($appid, $secret, $params['code']);