This is the login program from util-linux-2.4, modified to use
tcp wrappers
for authentication instead of /etc/securetty
(which is an admirable solution for multiuser machines with serial
connections to terminals, but modern environments appear to be
primarily tcp-ip connections to the machine.)
Login is not burdened with excessive portability or ease of configuration; it’s just a collection of files to download and compile. It’s stable (I use it in Mastodon Linux) and hasn’t been modified since the mid 1990s. It is composed of these text files:
Login is BSD-licensed except for the manual page, which is released under the GPL.