Problems with fingerprint-gui

I found a fingerprint reader when tidying up today and thought I’d have a go at making it work in Manjaro Cinnamon. I’d had one working under Ubuntu a few years ago and it worked well (for a time anyway).

The first issue I had was which pam file to edit since the guides assume Ubuntu and mention /etc/pam.d/common-auth (which doesn’t exist). I edited /etc/pam.d/system-auth as it seems like it’s included in other files in the hierarchy.

After this sudo & lightdm login were working fine with the reader.

The next issue was the polkit agent. Installation puts it at /etc/xdg/autostart/fingerprint-polkit-agent.desktop, but it didn’t seem to start without adding X-Cinnamon; to the OnlyShowIn= line.

The guides assume there will be either polkit-gnome-authentication-agent-1.desktop or polkit-kde-authentication-agent-1 in /etc/xdg/autostart, but there’s no other polkit agent there on my system & I can’t see that there’s anything polkit related running apart from polkitd itself. However, after doing one successful gui authentication (only ever text, never fingerprint), the agent seems to crash (Process 91461 (fingerprint-pol) of user 1000 dumped core.).

I also get this message in ~/.xsession-errors:
Cannot register authentication agent: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: An authentication agent already exists for the given subject

I’m assuming that polkitd is the service that these ‘agents’ interface with & it’s producing this error, but if there’s a conflicting agent I don’t know where it is.

Might just be time to revert all of this, but I was curious if anyone has it all working (especially non-Gnome/KDE setups).

Edit: also the strategies Sublime Text and Visual Studio Code use to edit files owned by root, don’t work any more! Ugh.