Authentication across Applications?

Hello,

 

I'm having difficulty understanding how this works.

I'm currently using VS2005, ASP.NET 2.0 and a SQL for the ASPNETDB database

I have successfully created users and roles on the ASPNETDB using "WebApp_A".

Now I wish to have "WebApp_B" be able to use the roles and permissions that I've set up on "WebApp_A"

My understanding is that I need to use the MachineKey element in the root web.config file?

But, how does this all work???

Here's what I'd like to be able to do.:

 

I'd like the user to try to request a web page from "WebApp_B" (from a link or url), but if they are NOT already Authenticated, I'd like to have them redirected to the to the "login" form from "WebApp_A".

I'd like the user to be able to supply the username and password there, have "WebApp_A" do the v ...