Modify another php session

index.php

<?php
session_start();
var_dump(session_id());
echo '<br>';
echo '<pre>';
print_r($_SESSION);
echo '</pre>';
?>
<hr>
<a href="login.php"><button>Login</button></a>
<a href="logout.php"><button>Logout</button></a>
<a onclick="logout_user();"><button>Logout User</button></a>
<a href="reset.php"><button>Reset</button></a>
<script>
function logout_user() {
    window.location.href = "logout.php?target="+prompt('User Session Id');
}
</script>

login.php

<?php
session_start();
$_SESSION['logged_in'] = '1';
header('Location: index.php');

logout.php

<?php

if (empty($_GET['target'])) {
    session_start();
    unset($_SESSION['logged_in']);
} else {
    // Save our id so we can revert to it later
    session_start();
    $old_id = session_id();
    session_write_close();

    // Modify targets session
    session_id($_GET['target']);
    session_start();
    unset($_SESSION['logged_in']);
    session_write_close();

    // Reset session id to ours
    session_id($old_id);
    session_start();
}

header('Location: index.php');

reset.php

<?php
session_start();
session_regenerate_id();
header('Location: index.php');