Comment # 3 on bug 1046959 from Josef M�llers

(In reply to Gordon Ashley from comment #2)
> cat /etc/pam.d/sudo
> 
> #%PAM-1.0
> auth     include        common-auth
> account  include        common-account
> password include        common-password
> session  include        common-session
> session  include        pam_xauth.so
           ^^^^^^^
There's the culprit! Change this to "optional".

> this file is default after new install. I did not change it.

I'll check where this comes from. It's definitely wrong.

> I've created a dummy file:
> 
> cat /usr/lib/pam.d/pam_xauth.so

When you change the "include" to "optional", this will be fixed as well:

> (location taken from strace log). Now I can sudo -u user and get no error,
> however X credentials are not forwarded.

I'll need to install 42.3 to see what happened. For the time being the solution
is stated above.

Josef