I guess this comment was originally a response to a different problem, but in my case it wasn't a "hack" - there was no problem with enabling federation on a private instance, and it worked as expected. I thought of a "private instance" as "can't see it unless you log in, but federates exactly like a public instance would", and that's exactly how it worked in 0.17.4, but I understand if, in principle, it wasn't supposed to work like that. Again, there was no need to hack anything on my end, it just worked.