single sign on

1. We have an application intranet/internet.
2. It is hosted in public IP
3. We would like to implement single sign on for that application
4. If the users are from within the organization we should get the login
credentials of the user
5. I should kept anonymous access only ( because it should work over
internet )
6. Is it possible to get the information?
7. What is Kerberos authentication? Will it be useful for me?