The Yale CAS client distribution includes modules for Apache which serve as a CAS 1.0 casclient. See AuthCAS for an alternative implementation of an Apache module for CAS authentication which offers additional features.
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Please note this is not extensively tested at this time. I believe there is still a little bit of work to be done. We plan on testing this here at Athabasca University within the next little while (currently May 27th, 2005). This modification was written by Trenton D. Adams and anonymous. If someone knows who anonymous is, let me know. I will search my email soon to see if I can find out who it was that helped me. We will soon contribute a binary RPM as well as a source RPM, which will automatically suck down the patch, and build against it.
*TODO : * support multiple certificate files in PEM format by using multiple directives.