Documentation of possible "key" values when using urbackupclientctl set-settings

I see that when using urbackupclientctl I can configure the values for several “key” variables. E.G.

urbackupclientctl set-settings \
-k internet_mode_enabled -v true \
-k internet_server -v "$URBACKUP_SERVER_NAME" \
-k internet_server_port -v "$URBACKUP_SERVER_PORT" \
-k computername -v "$URBACKUP_CLIENT_NAME" \
-k internet_authkey -v "$URBACKUP_CLIENT_AUTHKEY"

However, had I not found the above in a script included in the software, I never would have learned of these possible values for the ‘-k’ argument. I’ve looked in the Admin manual and don’t see documentation for this there.

How do I find out all of the possible variable names which ‘-k’ accepts and makes use of?
E.G. Is there another -k value which is used to specify what the restore key is (separate from specifying the internet auth key)?

urServer version: 2.4.12_amd64 (https://github.com/uroni/urbackup-server-docker)
urClient version: 2.4.10_amd64 (https://github.com/uroni/urbackup-client-docker)
Operating system: Linux and Docker.
Filesystem: external storage: ntfs. internal storage: ext4