public static function handle_signup()
 {
     $params = $_POST;
     $user = new User(array('username' => $params['username'], 'password' => $params['password']));
     $errors = $user->errors();
     if (count($errors) > 0) {
         Redirect::to('/signup', array('errors' => $errors));
     }
     if ($user->check_username_exists()) {
         Redirect::to('/signup', array('errors' => array('Käyttäjätunnus on jo olemassa')));
     }
     $user->save();
     $_SESSION['user'] = $user->id;
     Redirect::to('/', array('message' => 'Tervetuloa takaisin ' . $user->username . '!'));
 }