I recently setup a demo machine for a presentation on pxe boot, where I wanted people to be able to login and have a look around a demo pxe boot VM.
Lots of ways to do this, but the way I wanted to make this work was via ssh, without requesting a password.
To do this, I configured sshd with:
and configured /etc/pam/sshd, to allow members of the demo group access, by adding the following line:
auth sufficient pam_succeed_if.so user ingroup demo
then I just add users, and put them in the demo group if I want them to login without a password.. neat.