page.php

<?php
    session_start();

    if(isset($_SESSION['id'])) {
        $username = $_SESSION['username'];
        $userId = $_SESSION['id'];
    } else {
        header('Location: index.php');
        die();
    }
?>

<!DOCTYPE html>
<html>
<head>

    <title> / </title>

</head>
<body>

    <h1>Successfully logged in!</h1>

    <form methode="POST" action="logout.php">
        <input type="submit" name="logout" value="Logout" />
    </form>

</body>
</html>