Added casPassThrough. By default false, in case this set to true it will
pass the request through the filter chain instead of issuing a redirect.
This is make cas proxy authentication work when cas proxying is
initiated from a java client application.

As the ClientFilter is more generic (i.e. used for authentication
mechanisms than Cas) probably a tighter check is required. One approach
may be to check for presense of CasProxyProfile in the
principalCollction but would require a dependency on pac4j-cas which is
not there at present.