Grabbing file descriptors with pidfd_getfd()

Thanks for pointing to those!

However, I'd have reservations about using authbind - LD_PRELOAD is handy for debugging and trying weird tricks out, but I'm wary about using it in production systems.

innbind looks much cleaner, and certainly would allow you to write a program that could bind to privileged ports without needing to run as root, but as far as I can tell it allows any program on the system to bind privileged ports. If you installed it so that only members of a specific group were able to run it, and limited which programs ran as members of that group, that could work.