CAS has dependencies for the build. These are not presently documented.
yum install httpd-devel openssl-devel
On Centos 5.2 x86_64 there is a "bug" that does not install both the 64bit and 32bit apr-devel packages. Only the 32bit edition is installed by default. So you must then
yum install apr-devel.x86_64
The "bug" stems from the .pc files failing to declare dependency in the apr package itself.
The ./configure; make; make install method then does the trick.
Using apxs requires that you declare a number of environment variables/directories on the build line. Not an "easy" way to do it.