X-Win32 and FastX integrate with putty and pageant which allow CAC smarty card authentication.
For information and download for PuTTY-CAC, please go to https://gsallewell.github.io/piv-guides/windows/puttycac-install.
After installing and setting up PuTTY-CAC, make sure that pagent.exe is running.
Then launch your X-Win32 or FastX Session as needed.