Interesting little issue on the way: I didn't find a way to convince #guacamole to connect to a #guacd bound to ::1, but using the local #fqdn, so #x509 certificate validation is successful. OTOH, guacd configured to listen on "localhost" only binds on ::1 (no #IPv4!) as soon as #IPv6 is available. Weird.

As this is only on the local loopback interface, I'm fine for now forcing IPv4 here by configuring guacd to listen on 127.0.0.1 🙄