Hi @lucas_a.tx,
I managed to shutdown from the container without password by using the scripts mentioned above, running with the user root but creating the shared file inside /var/run/shutdown_signal as torizon user:
sudo -u torizon sh -c 'echo "waiting" > /var/run/my_dir/shutdown_signal'
thus I can write over it from inside the container.
Thank you.
Giulio