Unlock your Mac by entering a PIN on the touchpad. You may use this module to extend or replace the default password login. This is just a proof of concept and probably lacks security.
The touchpad is divided into a 3x3 grid which holds the digits from 1 to 9. The PIN was 1612 in this case. You don't need to actually click, just touch the pad.
Just run make.
Place pamtouch.so somewhere (e.g. /usr/local/lib/security/) and add a line for it in your pam configuration. There are multiple files for different purposes like screensaver or sudo. I was not brave enough to test it with /etc/pam.d/authorization.
leons-mbp:pamtouch leon$ sudo cat /etc/pam.d/screensaver
# screensaver: auth account
auth optional pam_krb5.so use_first_pass use_kcminit
auth required pam_opendirectory.so use_first_pass nullok
auth required /usr/local/lib/security/pamtouch.so
account required pam_opendirectory.so
account sufficient pam_self.so
account required pam_group.so no_warn group=admin,wheel fail_safe
account required pam_group.so no_warn deny group=admin,wheel ruser fail_safe