fprintd
Enrollement
sudo fprintd-enroll $USER
sudo fprintd-enroll $USER --finger right-middle-finger
Beware that just sudo fprintd-enroll confusingly also does work,
but that sets the fingerprints of the root user, which is not
what you'll want.
Configuration
Enable extra fprintd configuration with services.fprintd-extra.enable = true;.
You can adjust the allowed fingerprint authentication attempts before falling back to password input using:
services.fprintd-extra.maxTries = 10; # Defaults to 10 attempts