Xauth file written to /tmp by sddm. Why?

This is a continuation of the old thread “Sporadic failure to open display” by @JamesT from Aug `23. I found out that, at least on my system, the X authorisation file is written to /tmp. When I do not log off for 10 days, a daily system cron job cleans the directory, with subsequent authorisation failures for all X clients. That file is created by sddm:

Jan 29 17:52:46 asok sddm[948]: Xauthority path: "/run/sddm/xauth_PWrmHu"
Jan 29 17:52:46 asok sddm[948]: Using VT 2
Jan 29 17:52:46 asok sddm[948]: Display server starting...
Jan 29 17:52:46 asok sddm[948]: Writing cookie to "/run/sddm/xauth_PWrmHu"
Jan 29 17:52:46 asok sddm[948]: Running: /usr/bin/X -nolisten tcp -background none -seat seat0 vt2 -auth>
xauth -v list  
Using authority file /tmp/xauth_GnZgjo
asok/unix:0  MIT-MAGIC-COOKIE-1  b3d77bf8c01624ed871aa08e6a2b7a21
#ffff##:0  MIT-MAGIC-COOKIE-1  b3d77bf8c01624ed871aa08e6a2b7a21

I do not have ~/.Xauthority.

On my laptop, with the same version of Manjaro, I start up with multiuser run level, then run startx. That creates ~/.Xauthority (there is no relevant entry in the journal):

xauth -v list
Using authority file /home/george/.Xauthority
zenbook/unix:0  MIT-MAGIC-COOKIE-1  e17dabf96518745fde9f33fd92746e40

So, is this a feature or a bug of sddm?

Feature.

OK, thanks. So, to avoid having to reboot every 10 days, I copied /var/lib/tmpfiles.d/tmp.conf to /etc/tmpfiles.d and increased the cleanup value to 30 days. Hopefully this is going to work.

Don’t know for sure it this will work but I’ve tried adding:

30 2 * * * touch /tmp/xauth*

to my crontab.