How to pass session cross different domains?

Now i am working on an cart application, when i add an item to cart(in the domain of, and then checkout(in the domain of, i still want to get the item from the cart. I used the plugin of ssl requirement, and i append the host and session_id into

the checkout url, as checkout it would redirect to Now the problem i could not get the data from the session.

Further more, i used memcached as session store. Is there anyone met this problem ever?