<?php
session_start();
$pwd="12345";
if(!isset($_SESSION["lgn"])){
    if(isset($_GET["pass"]) and $_GET["pass"]==$pwd){$_SESSION["lgn"]=1;header("Location: ?");}
    echo "<form method='get'>Password: <input type='password' name='pass' /> <input type='submit' value='Login'></form>";
    die();
}
?>