You can do `grep` under `/opt/shibboleth-idp/` for "The logout operation is complete" to see where it comes from. The rest is more a coding kind of task, hardly related to Gluu Server itself. You basically will need to figure out layout of this page and edit it accordingly. That's not something we can offer support for in Community Support. You may find more helpful tips asking on Shibboleth-related forums, as well.