Untitled

<?php
session_start();
if(!isset($_SESSION['username'])){
        $user = $_POST['user'];
        $pass = $_POST['pass'];

        $account_user = "test";
        $account_pass = "test";

        if($user==$account_user && $pass == $account_pass){
                $_SESSION['username']=$user;
                echo "Logged in!";
        }else{
                echo "Wrong pass/user!";
        }
}else{
        echo "You are already logged in ".$_SESSION['username'];
}
?>