Allow CAS 3.0 endpoints (/p3/serviceValidate and /p3/proxyValidate)
CAS 3.0 now uses /p3/serviceValidate and /p3/proxyValidate: https://apereo.github.io/cas/5.1.x/protocol/CAS-Protocol-Specification.html
The CAS response is the same than CAS 2.0, so it is easy to accept these new endpoints.