At work we run a fairly large extranet SharePoint farm where some sites are anonymous access. Normally in SharePoint, when a domain user on a domain workstation hits a SharePoint site that requires authentication, it automatically logs them in. Unfortunately, in that same scenario but the site is anonymous, the user will not get logged in. The user then has to realize this and click sign in at the top right. Also because SharePoint security trims the user interface so you only see what you have access to see. Many times users will complain they have lost their permissions or something because they won’t be able to find their normal way of doing things when they don’t realize they aren’t logged in.
Anyway, here’s the code:
Here is what shows up in fiddler when someone is not logged in successfully, thus it falls back to anonymous. You can see that the authentication doesn’t happen and blank.gif is never called.