Joomla woes

[eluser]jwindhorst[/eluser]
Hi all, it's been a while since I've posted but this ones a good one.

Our company has decide to use Joomla for their CMS and CI for the application. Now however, they want us to come up with a way for our application login to work on both domains. application.com and cms.application.com. So fine, our sessions are stored in the DB so we can use the end users IP to locate their session record regardless of the domain, but I cannot find where Joomla checks for a user and creates it.

I'm thinking it's hidden under a meatball in the nonsensical spaghetti mess of code Joomla uses. Anyone have any ideas where this might be? Or a better way to accomplish the same goal? We're using the new release of Joomla, 1.5.whatever.

Thanks