Answer
This is normally handled automatically as long as the server's AD domain matches and DNS resolves the FQDN correctly — if it isn't working, the fix path is the 'System Access Setup' screen: with SSL Passthrough enabled, you can specify a secondary FQDN there (this is specifically intended for external access via a load balancer FQDN that differs from the server's own actual name). Underneath, this is controlled by Oracle HTTP Server's own configuration files — those can technically be edited by hand, but doing so isn't recommended or supported, since manual changes get overwritten the next time the environment is reconfigured.