It may be desirable to have touch on the login screen.

This is supported with UPDD but there are a few considerations.

With the extra security added to MacOS 10.14 Mojave you now have to grant the driver permission to control the computer in the Security & Privacy dialog as described here.

To log on to the Mac system you likely need to select the user account and enter the password. Up until 10.14 you need a physical keyboard to perform any data input on the login screen. We have been unsuccessful in utilising any virtual keyboard on the login screen.

Starting with 10.14 you can enable the Accessibility keyboard on the login screen as described here.