Yaf_Session::set

<?php
class LoginController extends Yaf_Controller_Abstract
{
    public function indexAction()
    {
        // ... verify the credentials against the database
        $session = Yaf_Session::getInstance();
        $session->start();

        $session->set("user_id", $user->getId());
        $session->set("login_time", time());

        return $this->redirect("/dashboard");
    }
}
?>