GDM fingerprint authentication with systemd-homed

Almost a year ago I acquired a thinkpad p1 gen 3 from my employer, and installed Arch with GNOME. As with every install, I wanted to play with what was new in the linux world so I set up my user account using systemd-homed as a BTRFS subvolume (not an encrypted luks loopback). For the most part this has worked out ok.

Recently, I wanted to set up the fingerprint reader so I installed and enabled fprint. Theoretically this is supposed to enable the fingerprint enrollement UI inside GNOME settings without further configuration. It did not. I was able to register a print with fprint-enroll and the effects are:

  • fprint-verify works
  • GDM prompts that I can use fingerprint to log in, but attempting to do so always fails
  • The GNOME lock screen also prompts that I can use fingerprint to unlock, and that works fairly reliably (the sensor itself seems finicky, which squares with what ive read of others’ experience with thinkpad fingerprint readers)
  • systemd-ask-password prompts (such as when running a systemctl command without sudo, which display via GNOME UI) do not offer fingerprint authentication, nor does it work if i try to press the sensor anyway
  • GNOME settings still shows nothing in relation to fingerprint auth in the user management section

I’ve searched around a bit and I haven’t been able to find anything about this issue from other users, so I’m hoping someone around here has some experience with this odd combination of fingerprint auth, GNOME and systemd-homed that can provide some insight.

Fail that, it’s quite difficult to figure out where exactly to open an issue among all of the gitlab repositories so maybe some pointers there would be helpful.

tl;dr fprint + systemd-homed doesn’t seem to be picked up by GNOME authentication prompts consistently. Unsure where to report.

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  • fprint-verify works

Then fingerprint works.

  • GDM prompts that I can use fingerprint to log in, but attempting to do so always fails

This cannot work.

  • The GNOME lock screen also prompts that I can use fingerprint to unlock, and that works fairly reliably (the sensor itself seems finicky, which squares with what ive read of others’ experience with thinkpad fingerprint readers)

Depends on the reader, the synaptics prometheus ones should work quite well.

  • systemd-ask-password prompts (such as when running a systemctl command without sudo, which display via GNOME UI) do not offer fingerprint authentication, nor does it work if i try to press the sensor anyway

What are you expecting there? A fingerprint is not a password.

  • GNOME settings still shows nothing in relation to fingerprint auth in the user management section

That one is the only thing that actually seems wrong in your description. Run gnome-control-center in a terminal to see if there are errors. Also, check whether the fprintd-* utilities work fine when running as your use (i.e. without sudo).

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