Autologin when pam allows

I am not sure how correct my request is, but for example standard lightdm greeter allows you to login without entering your password when some pam module gives you sufficient rights to do so.

So when you have some pam module with 'sufficient' qualifier (or how it is called) and that module gives you permissions without interaction somehow, you can have such button or just automatically log in.

In my case it's pam_usb - on Ubuntu when i plug my USB key (with pamusb.conf configured for my user ofc) in it shows just Log in > button in place of password field.