In the default graphical environment, smart card authentication
can be enabled on the login screen by setting enable-smartcard-authentication
to true.
To enable, add or edit enable-smartcard-authentication to
/etc/dconf/db/gdm.d/00-security-settings. For example:
[org/gnome/login-screen]
enable-smartcard-authentication=true
Once the setting has been added, add a lock to
/etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification.
For example:
/org/gnome/login-screen/enable-smartcard-authentication
After the settings have been set, run dconf update.