Listens to your Yubikey being removed and locks your mac.
Installs a LaunchAgent for your user that will listen to the Yubikey being removed and call a non-public Apple API to lock your screen. Don't even think about putting this into the AppStore, it will never be approved b/c of the internal API.
make → Compile lockscreen binary
make install → Install lockscreen and load LaunchAgent
make remove → Remove lockscreen binary and LaunchAgent