SEC-2127: Support multiple hostnames

Condor (Migrated from SEC-2127) said:

I have 3 related problems with the Spring Security CAS client:

1. My web application is accessible on multiple host names and after logging in the CAS server should redirect to the original host and not one single host as specified in the service config option.
2. I patched the code to use the host and port of the original request, but then I noticed that the request url was also wrong because my application server is behind a proxy server. So I modified the patch to also use the X-Proxy-Host header when available.
3. I configured my CAS server to allow a service parameter for redirect after single sign out. Spring Security CAS has no standard logout handler for this, so I created one and I had to add the same service url processing as #2.

This all works, but I assume that more people are having this problem. So I would like to request that these feature are added to the library. Thanks.

Start by reviewing the Spring Security CAS client’s service URL handling and logout handling described in the issue. Trace how the original host, port, proxy host header, and service parameter are processed, then verify behavior for multiple hostnames, proxied requests, and single logout redirects.