Azure AppFabric ACS - Unauthorized: Logon failed due to server configuration
While I was playing around with Azure AppFabric ACS I got the following error:
Error message 401.2: Unauthorized: Logon failed due to server configuration. Verify that you have permission to view this directory or page based on the credentials you supplied and the authentication methods enabled on the Web server. Contact the Web server's administrator for additional assistance.
This error only occured when using ACS in a regular Web Forms application in IIS. But for ASP.NET MVC applications everything worked perfectly. To get my Web Forms application working I had to to turn a Windows feature on: IIS Metabase and IIS 6 configuration compatiblity
After updating the IIS installation the Web Forms application worked perfectly using Azure AppFabric ACS authentication. If you're doing this on Windows Server 2008 you can simply modify the Web Role.
Enjoy