In Trusty, there is a new lockscreen that fits the look and feel of lightdm, and shares some config files, especially for pam.
I am using
libpam-fprintd to allow using my fingerprint reader when asked for a sudo password, or for unlocking the screen.
The point is that I don't want to allow the fingerprint reader when logging into the desktop. But I want to allow it when unlocking the screen. The reason for that is that fingerprint won't allow to open the gnome-keyring, which is fine when unlocking, but not when loging-in. This also enables me to have a strong password, as I type it only once, then use the fingerprint reader.
See the PPA page instructions, especially the "Note on keyrings and passwordless logins" part
Before the new lock-screen,
/etc/pam.d/lightdm was used by the greeter, not by the (old) lock-screen. So I had a different behaviour when logging in and when unlocking, which was exactly what I wanted.
See this page from the Thinkwiki for the config used.
Now, it seems that
/etc/pam.d/lightdm is used by both the greeter and the lock-screen.
So my need would be to have a distinct pam config file for the greeter and for the lock screen. Is this possible?