Use CAS protocol 3.0 for service validation
Use CAS protocol 3.0 for service validation

This is only meant as an example. Revert this commit and add a config
option instead. Examine the URI overview at
http://jasig.github.io/cas/4.1.x/protocol/CAS-Protocol-Specification.html#cas-uris
to see what endpoints change between protocol v2.0 and v3.0.

FronteraConsulting/rack-cas,biola/rack-cas