PHP獲取小程序用戶openid

代碼如下：

//code值，從前端獲取
$code = $_GET['code'];

//注冊時獲取
$appid="xxxxxxxxxxxxx";
$secret = "xxxxxxxxxxxxxxxxxxxxx";

$get_code_url = 'https://api.weixin.qq.com/sns/jscode2session?appid='.$appid.'&secret='.$secret.'&js_code='.$code.'&grant_type=authorization_code';
$ret=file_get_contents($get_code_url);
$openid= json_decode($ret)->{'openid'};