I'm attempting to get CSSC to perform an authentication against our ACS database using Single Sign On. However, I need the username to be passed to ACS as DOMAIN\USERNAME whereas CSSC appears to pass just the USERNAME portion. ACU/ADU have the ability to include the domain name in the logon, but I can't see a similar option in ACS. (The DOMAIN portion needs to be included as some users already exist in the ACS database as token-based users with the same USERNAME).
The documentation suggests it is possible to alter how the SSO details are passed to the authentication server, but I cannot find what the documentation refers to as the "SSO text entry box".