As other people say, you cannot share cookies, but you could do something like this:

1. centralize all cookies in a single domain, let's say cookiemaker.com
2. when the user makes a request to example.com you redirect him to cookiemaker.com
3. cookiemaker.com redirects him back to example.com with the information you need

Of course, it's not completely secure, and you have to create some kind of internal protocol between your apps to do that.

Lastly, it would be very annoying for the user if you do something like that in every request, but not if it's just the first.

But I think there is no other way...