Keeping Sessions Scross Multiple Domains?

I have a forum which has used VBSEO since it was first released, at Apex Community Forums and it has been great. I want to do something but don't know the right way to go about accomplishing it. Maybe someone has some advice.

ForumApex.com is the discussions forums for PCApex.com and GameApex.com. How can I arrange it so if a member signs in at any of those 3 sites, he stays logged into them when surfing around all of the sites? I am open to ALL suggestions.

I will also be using the wordpress bridge as our new CMS. either one CMS for both somehow or a seperate install for each of the content sites. What do you think?

This is a near impossible task, and i don't think anyone has it working. at least i haven't seen it...

The problem is, cookies can only be set for the domain you're on.

the only way to do this would be to
A) have the exact same member database for all sites (which means, you need to hack all 3 sites to make this work... and since they're already established, you would have to merge all 3, then de-doupe to get a common demonitator. But, you're screwed if someone uses a different login on another site.)
B) on login, call hidden iframes that are remote linked from the other domains that set a successful login cookie for them too.

B is very possible.

Both of the sites already use forumapex as their forum and member-base.

Is it possible to just host all of the sites on one domain and assign the domains to certain directories on the main domain? Use all the other domains as aliases and point them only to certain directories on the main site? Then it is just a matter of using the correct site skin on the articles in each directory and linking mainly within that domain (which is really just an alias for the main domain).

So, basically, everything will be run on one site and then the two review-based sites gameapex.com and pcapex.com will be aliases for forumapex.com (the main site that will host the forum and wordpress bridge). VBulletin allows you to setup aliases as well in the AdminCP so I am guessing that would cover my cookie issue if everthing is setup like this, correct?

it's possible, but vb doesn't support it naively.

there's a mod to use one source for your files across multiple instances, but its tricky to set up.

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