X11 forwarding from an OpenIndiana Zone

For testing, I installed a zone on OpenIndiana Build 151.
(zonecfg, zoneadm install ... )
Logging in via ssh works over a crossbow switch. /etc/ssh/sshd_config is configured
to allow X11 Forwarding, but a ssh -X call fails.

Enabling debugging of ssh with ssh -Xv showed, that xauth is missing in the zone.
pkg install xauth 

solved this issued for me.