can I use Form Authentication in my scenario?

Hi, I am new to the ASP.net world, I am working on an application, where authentication information will come from different sources, and I want certain pages only to be displayed to certain groups or role. Its kind of complex algorithm, and I have written a class for it,and all I need to call necessary function during authentication. Obviously, I wont be using default membership database for asp.net. So I am wondering if I can use Form Authentication in my scenario? If yes, then can give me hint on how can do this or point to appropriate resource? I can do it old way, like setting up required session values and check it in every page but I think there must be better way of doing it.
Thank you
Arya

Note: user authentication and role will be coming from different source ...