Co-existence with ASP.NET Membership?

We have a IIS7 server with several different ASP.NET applications. We would like to use a single membership database för all of these applications.

Today we have one user base for FileVista and another (ASP.NET Membership) for the other applications. 

Would it be possible to use the FileVista database as a ASP.NET Membership database? It would make life a lot easier for us and probably for otherts as well if one could re-use the membership database for other webb applications.

If not, how can I pre-autenticate a user that is already logged in using ASP.NET Membership? Can I pass on the username and a password token? Any suggestions are much appreciated!

There is already a feature called pass-through login for this purpose, please see the below topic for more information on this feature:
Pass-through login