Forms Authentication across Sub-Domains

Question

Is it possible to authenticate users across sub-domains when the authentication takes place at a sub-domain instead of the parent domain?

For example:

User logs into site1.parent.com, and then we need to send them to reporting.parent.com.

Can I authenticate them to the reporting site even though the log-in occured at a sub-domain?

So far all of the research I have done has users logging into the parent domain first and then each sub-domain has access to the authentication cookie.

Answer 1

In addition to setting a cookie to parent domain also need to make sure that all sites (apps) have same validationKey and decryptionKey () so they all recognise each other's authentication ticket and cookie. Pretty good article here http://www.codeproject.com/KB/aspnet/SingleSignon.aspx