Sharing Authentication between ASP.NET sites

Question

I have two ASP.NET sites (they can not run in the same process) and I need to share authentication between them. If a user is in site A already authenticated and then goes

Answer 1

Are they in the same domain?

If you have app1.blah.com and app2.blah.com, it's very easy to do. Just set the domain and the name to the same value in the forms-section in web.config:

An added benefit is that users can sign into either site and will still be authenticated if they go to the other one.