[Typo3-dev] Authentication Services: Detect session across multiple sites

[Christian Melchior]

Hi

I'm working on a project where a user login is working for several
independent Typo3-sites.

User data is stored on a seperate server, and I'm using Authentification
Services to get to these data - which works like a charm.

But how do I get Typo3 to detect a existing login from another site?
I have thought about extending cc_sv_auth so it can alter/create a 
typo3-session but I'm not sure if this is the right place to do it?

Hope someone can help with this,
Christian Melchior