Debian Live flatpak integration?

[Ronny Standtke <ronny.standtke@gmx.net>]

Hi all

We are providing some local schools here with customized Debian Live
images. Usually they are a combination of Debian stable and some
selected backports (LibreOffice, Linux kernel, ...). Now we have some
schools that really want to use the current versions of GIMP and
Kdenlive. Both packages are not up to date in stretch-backports, but are
available as flatpaks on flathub, see:

https://flathub.org/apps/details/org.gimp.GIMP
https://flathub.org/apps/details/org.kde.kdenlive

Now that flatpak 1.2.3 has arrived in stretch-backports, I wanted to
integrate the GIMP and Kdenlive flatpak packages in our Debian Live
builds. Unfortunately, calling flatpak in a live-build hook fails with
some dbus and polkit error messages. Here is an example that just tries
to add the flathub repo:

cat config/hooks/live/add_flathub.chroot
#!/bin/sh
flatpak remote-add --if-not-exists flathub
https://flathub.org/repo/flathub.flatpakrepo

After adding this hook live-build fails with the following error message:

-------------------------------
P: Begin executing hooks...

(flatpak remote-add:9603): GLib-GIO-CRITICAL **:
g_dbus_connection_register_object: assertion 'G_IS_DBUS_CONNECTION
(connection)' failed

** (flatpak remote-add:9603): CRITICAL **:
polkit_authority_register_authentication_agent_with_options_sync:
assertion 'POLKIT_IS_AUTHORITY (authority)' failed
Segmentation fault
E: config/hooks/live/add_flathub.chroot failed (exit non-zero). You
should check for errors.
P: Begin unmounting filesystems...
-------------------------------

I tried prefixing the call to flatpak with dbus-run-session, but it
still fails.

Is there any dbus/polkit trick to be able to call flatpak in a
live-build hook?

Best,

Ronny