PHP VK.com oAuth Login Demo

<?php
session_start();
include("vkapi.class.php");
if($_GET["logout"]){$_SESSION[user_id]=null;}
$appid="2773137"; $settings="photos"; $secret="<....>";
$api=new vkapi($appid,$secret,$_SESSION["access_token"]);
if($_GET["callback"]){
    $req=$_REQUEST["code"];
    $data=$api->token($req);
    if($data['access_token']){
            $_SESSION['access_token'] = $data['access_token'];
            $_SESSION['user_id'] = $data['user_id'];
            echo "<html><body onunload='window.opener.location.reload(true);'><script>window.opener.location.reload(true);window.close();</script></body></html>";
            exit();
        }
}else{
    if($_SESSION["user_id"]!==null){$login=1;}else{$login=0;}
}
?>
<!DOCTYPE HTML5>
<html>
 <head>
  <title> LogIn </title>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
  <script>
  var appID = "<?=$appid;?>";
  var settings  = "<?=$settings;?>";
  var redirect  = "http://local.lc/vk.php?callback=1";
  window.onload=function(){
        url='http://oauth.vkontakte.ru/authorize?client_id='+appID+'&scope='+settings+'&redirect_uri='+redirect+'& display=popup&response_type=code';
  }
  </script>
 </head>
 <body>
 <?php if($login==0){?>
  <button id="login" onClick='window.open(url,"vkauth", "location,width=620,height=320,top=0");'>Log in via VK.com</button>
  <?php }else{ ?>
  Hello, id<?=$_SESSION["user_id"];?>.<br />
  <?php } ?>
 </body>
</html>