dynamic callback urls

Hi, I made some changes mainly to pac4j-core and pac4j-cas to support non absolute callback urls. I have a situation where my application can be served up through multiple domains (whitelabeling). So, for example, I can access my application by going to brand1.com or brand2.com. So I want to be able to dynamically set the CAS login and callback urls based on whatever the current host/domain is. It would be great if you could merge these changesets in if you think they are ok. Please let me know if you want something done differently and I'll make the updates.