gistfile1.php

function signin_required($login_page, $fn) {
    return function($db) use ($fn, $login_page) {
        if (array_key_exists('user_id', $_SESSION))
            $fn($db);
        else engine\redirect($login_page);
    };
}

gistfile2.php

engine\run([
    'get:'          => $login_form,
    'get:login'     => $login_form,
    'post:login'    => $do_login,
    'get:home'      => $home,
]);