How can I let a user log in on one PC only?

How can I let a user log in on one PC only?

Hello,
I am writing a Zenon system which will have 2 servers to talk to the PLCs and two clients which both run the same program.
I need to make sure that a user can only log-on on one of the clients at any time. The other PC should then prevent log-on until the first is logged off.
Is there a simple way to do this?

This is a migrated post! Originally posted on 17.07.2017 by user mjackson. Please be aware that information can be outdated.