Share ASP.Net web application authentication with another web sites

Question

I have an large ASP.Net web application that will have a large number of users and I want to make this site accessible from other sites by take the credentials uses to have authentication to other sites on another domains, to make it easy to understand from you the idea like this site we can access it by using Yahoo, Google or Facebook account

my web application use form authentications.

any Idea to do this

Thanks all

Answer 1

I have tried to find out the links which might help you in your course to support multi-website authentication :-

Facebook Authentication

Google Authentication

OpenId

Answer 2

If you use the passport authentication provider instead of the forms provider on your web site this would enable authentication across domains that support this. This works if you can implement this across your domains or you're using existing sites that already support this.