Keep in mind that a big part of the configuration complexity of CAS is because of how it's used and customized in the real world.

These kinds of infrastructure systems its very common to replace a bunch of the built in functionality with your own classes, and so there's alot of effort put into supporting that use case.

I helped build a large open source enterprise financial systems, and most of the deploying orgs used CAS for authN. Both CAS and the financial system was built with similar approach to extensibility.