Sharing session information between 2 domains?

Question

I am dealing with a booking engine, and I have an oddball specific request from the client.

Firstly though, there are two domains:

http://my-client.com/

and

http://booking-engines.com/my-client/

There exist 4 overall steps:

1. Check availability through a booking console ( specify criteria such as # of adults/kids/dates ). This lives on http://my-client.com/. It posts to http://my-client.com/search/
2. Select units and post to booking engine domain. This lives on http://my-client.com/search/ and POSTs to http://booking-engines.com/my-client/guest-information/.
3. The guest information page is where the user enters credit card, address, contact information and POSTs to make their reservation. This lives on http://booking-engines.com/my-client/guest-information/ and POSTs to http://booking-engines.com/my-client/book/
4. If the booking is successful, user is rerouted to http://booking-engines.com/my-client/success/ where the user may print the information out and it gives the user a confirmation number, etc.

Here's the key dilemma: On http://booking-engines.com/my-client/ which only holds steps 3 and step 4, there's navigation for the first and second steps, which have to link to the original site.

I am now using sessions on separate domains - is there a way to share sessions for two different domains in a semi easy way so that information can be retained without the user having to re-enter stuff?

Answer 1

Semi-easy would be posting the session data along with units in step 2. I'm assuming there's no sign on process that needs to be done on the server and that the data is not something that needs to be encrypted. If it is, post using https, is possible.

Not so easy would be setting up a shared database to store session information.