Set redirect after customer new registration issue in Magento

Question

I am using an observer with this event customer_register_success.I want to redirect my new customer to cart after the registration. This is my code from my observer:

$customer = $observer->getEvent()->getCustomer();
if ($customer){ // customer new registration after
   //Mage::app()->getResponse()->setRedirect($lastUrl); // This doesn't work
   Mage::app()->getFrontController()->getResponse()->setRedirect($lastUrl);
   Mage::app()->getResponse()->sendResponse(); // This works but the customer is not logged in.
}

If you check my comments from the code. How can i make the user to be redirected and to be logged in too ?

Thx

Answer 1

This piece of code did the job:

 Mage::getSingleton('customer/session')->setBeforeAuthUrl($lastUrl);