Apache with RADIUS (IAS)

Hi there,
I have an Apache 2.0.52 running on Red Had Enterprise Linux 4.
I have also a RADIUS server running on Windows Server 2003 (It's called
Internet Authentication Server (IAS) on Windows).

What I want to do is to configure the apache server with the IAS
authentication. But I have no idea to configure the apache with RADIUS.
Where should I start, or are there any good documents I can read from the
Internet?
Thanks in advance,
Ross