Recently had to restart a client’s server after running some Windows Updates. A few hours after the restart the client contacted me stating that they couldn’t access their e-mails via the web. I quickly had a look, the login page presented itself, so I logged in and after clicking Sign in I was presented with a blank page pointing to auth.owa. This was a little puzzling as there were no updates for Exchange so why did it break? Checking the IIS logs, I found that the error was 500 which indicated some kind of authentication error.
A little powershell cmdlet you can run is Test-OWAConnectivity. So I ran the cmdlet and recieved WARNING: An unknown failure occurred during logon. So I checked IIS and ensured that all of the authentication was set correctly and indeed it was. So after some poking around on the web I found out Exchange 2010 palms off the Forms Based Authentication to a seperate Service called Microsoft Exchange Forms-Based Authentication Service. Starting this service fixed the blank page issue and allowed clients to authenticate correctly.