Specific Client Access to Server via WAN

We’re looking to have a specific user access a folder on a server accross our WAN. However, we only want that specific user to be able to access the server via their personal workstation only. We don’t want them to be able to logon to someone else’sworkstation and access this specific folder on the server. Got any ideas that we can use to allow access on from that workstation? IP logging won’t work due to the use of DHCP. User verification and MAC logging??? Thanks!!!