I’ve looked everywhere to try to get it working, and I couldn’t find a guide that’s accurate. I finally found out a way to make Devise (warden based) to properly use the cross subdomain cookie. This method should work with ANY authentication engine though.

The way that’s supposed work but doesn’t work as of Rails 3 Beta2

So I had to force a default into the session store

You might want to have different domain settings for each environment. Go ahead and create a YML file and load it from there