I want to say that we have WebAuth working on 10.5.2, but it's not. At least not yet.
At issue is the changes undertaken in web services between 10.4 and 10.5. They're quite substantial.
Tiger's web server was Apache 1.3, was 32-bit and either built for PowerPC or, later, to be "universal" to additionally run on Intel processors. Leopard's web server is a whole other beast. The default web server is now Apache 2.2, it's all 64-bit and it's built for four different processor families.
betenoire:~ nbfa$ file /usr/sbin/httpd
/usr/sbin/httpd: Mach-O universal binary with 4 architectures
/usr/sbin/httpd (for architecture ppc7400): Mach-O executable ppc
/usr/sbin/httpd (for architecture ppc64): Mach-O 64-bit executable ppc64
/usr/sbin/httpd (for architecture i386): Mach-O executable i386
/usr/sbin/httpd (for architecture x86_64): Mach-O 64-bit executable x86_64
This will pose some challenges.
A lot of third party modules won't work, at least out-of-the-box.
But I've had a heck of a time getting WebAuth to bend to my will. I'm excited that Apache 2.2 is the default web server, which means I can use Server Admin to administer sites (well, for what it's worth). Previously, admins had to use the version included in /opt/apache2 in Tiger, because of WebAuth's dependency on Apache 2. Still, I haven't gotten WebAuth to compile cleanly or to built under the architecture of my Xserve (ppc64).
Here are the ugly bits from the webauth-info list. Blech.