I needed to get WebAuth working on my Leopard server, but out of the box, there are some issues with building the modules. I want it to work with the included Apache 2.2, so that I and other admins can use Apple's Server Admin tool to configure sites and directories. (Admittedly, I get that tingly, satisfying feeling when third-party tools fit like a puzzle piece in your operating system of choice. Can't discount that motivating incentive.)
But time pressures prevailed, so I had to prioritize a workaround to meet a looming deadline. Personally, "workarounds" almost always gives leave me dissatisfied, but in this case, it's a necessity. Here's how I implemented WebAuth, opting to give up the web server administration utility of Server Admin (which, at the end of the day, isn't too great a loss).
In short, you'll 1) build Apache 2.2 from source, 2) build WebAuth, 3) add the WebAuth Kerberos keytab, 4) add an SSL certificate, 5) hand-configure your conf files to protect your sites and 6) add a launchd file to start it all automatically.