php 获取微信用户的openId

// 这里的code是通过前端页面获取的
//$appid = "公众号在微信的appid";
//$secret = "公众号在微信的app secret";

public function userOpenId($appid,$secret,$code)
    {
        $url = "https://api.weixin.qq.com/sns/jscode2session?appid=$appid&secret=$secret&js_code=$code&grant_type=authorization_code";
        $curl = curl_init();
        curl_setopt($curl, CURLOPT_URL, $url);
        curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, FALSE);
        curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, FALSE);
        if (!empty($data)) {
            curl_setopt($curl, CURLOPT_POST, 1);
            curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
        }
        curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
        $output = curl_exec($curl);
        curl_close($curl);
        $data = json_decode($output,true);
        if (isset($data['openid'])){
            return $data;
        }
        return false;
    }