public function before()
{
    parent::before();

    if ( ! Session:;instance()->get('logged_in', FALSE))
    {
        $this->request->redirect('admin/login');
    }
}

public function action_login()
{
    if ($_POST)
    {
        $username = arr::get($_POST, 'username');
        $password = arr::get($_POST, 'password');

        if ($username == $this->_username AND $password == $this->_password)
        {
            Session::instance()->set('logged_in', TRUE);
        }
    }

    $this->template->content = View::factory('admin/login');
}