self.php

<?php
session_start();
$password = "passhere";

if( isset($_GET['action']) && $_GET['action'] == 'logout') {
    session_start();
    session_destroy();
    header("location: self.php");
    exit();
}

if ( (isset($_POST['mdp']) AND $_POST['mdp'] == $password ) OR $_SESSION['is_logged_in'] ) {
    $_SESSION['is_logged_in'] = true;
} else {
    $_SESSION['is_logged_in'] = false;
}


if ($_SESSION['is_logged_in']) {

    ?>
    <!--Log out button-->
    <a href="self.php?action=logout">Log Out</a>
    <?php

    if(isset($_GET['action']) && $_GET['action'] == 'save') {
        if(isset($_POST['txtpage'])) {
            $ttp = $_POST['txtpage'];
            file_put_contents("test.php", $ttp);
        }
    }

    $page = file_get_contents('./test.php', FILE_USE_INCLUDE_PATH);
?>

<!--Save form-->
<form id="send_form" action="self.php?action=save" method="post">
    <textarea rows="15" cols="50" id="txtpage" name="txtpage" ><?php echo htmlentities($page); ?></textarea>
    <input type="submit" value="Send"  />
</form>


<?php
} else {
?>

<!--Login form-->
<form action="self.php" method="post">
<p>
    <input type="password" name="mdp" />
    <input type="submit" value="Access" />
</p>
</form>

<?php
}
?>