To use Digest authentication in Internet Information Services (IIS) 6.0 when the domain controller is running Microsoft® Windows® 2000, you must enable subauthentication, which is not installed by default on IIS 6.0. There are three requirements for enabling subauthentication:
Install the subauthentication component, iissuba.dll.
Set the UseDigestSSP metabase property to False.
Set the identity of the application pool to Local System. For more information about setting application pool identity, see "Chapter 4" in this book.
Consider the following guidelines for enabling subauthentication:
The requirement to use subauthentication applies to Digest authentication only. Using Advanced Digest authentication does not require subauthentication. ...