cancel authentication process when screen turns off/greeter loses focus

[Yakumo Ran]

I have a fingerprint scanner which is blinking when system requires authentication. So when I lock my session the scanner begins to blink. I configured the greeter to turn off a screen in 10 seconds after lock but after 10 seconds scaner continues to blink because authentication process continues too.

This causes 2 problems:
1. It's a bit annoying because scaner blinks.
2. pam_fprintd has a timeout after which it finishes with failure. This means that I should press enter to fail pam_unix auth and run a new auth process to use the scanner.

This can be fixed if auth process was cancelled when screen turned off, and then restarted when screen turned on.

There is also another problem which I guess doesn't related to the problem described above. If I switch to another VT, it'll requre from me auth as well. But I can't auth using scaner from VT because it has been aquired by greeter auth process (scanner cannot be used by 2 processes at the same time).

This also can be fixed if auth process was cancelled when VT switched, and then restarted when I switch back to greeter.