in the xfce4-session manual you make an example how to configure sudo so that other users can shutdown/reboot the system. you quote this example: myuser myhost=/usr/local/libexec/xfsm-shutdown-helper however, this won't work, because sudo wants to have the users password, but xfce-session can't handle this (can it?)... instead, the sudoers entry should be: myuser myhost= NOPASSWD: /usr/local/libexec/xfsm-shutdown-helper no big thing, but took me a few (annoying ;-) minutes... Reproducible: Always Steps to Reproduce: 1. 2. 3.
xfce4-session can ask the user for a password. If it doesn't work for you, then thats a bug in xfce4-session. Anyways, the manual is right here.