<?php 
session_start(); 
  
$user=""; 
$pass=""; 
  
if(isset($_POST['submit'])){ 
  if($_POST['user']==$user){ 
   if($_POST['pass']==$pass){ 
    $_SESSION['username']=$user; 
    }else{ 
    exit("Wrong User/Pass!"); 
    } 
  }else{ 
  exit("Wrong User/Pass!"); 
  } 
} 
  
if(!isset($_SESSION['username'])){ 
 echo "<form action="" method="post"><center> 
 <table><tbody> 
 <tr><td>Username: </td><td><input type="text" name="user" value=""></td></tr> 
 <tr><td>Password: </td><td><input type="password" name="pass" value=""></td></tr>
  <tr><td colspan="2"><input type="submit" name="submit" value="Login!"></td></tr>
  </tbody></table></form></center>"; 
exit(); 
} 
  
if(!isset($_SESSION['username'])||$_SESSION['username']!==$user)){ 
exit(); 
} 
?>