Slim, the SliTaz Login Manager asks for a password when a special command like halt, reboot or shutdown was entered in place of a user name.
The required password is that from user root!
Enter the root password and the appropriate action for halt, reboot or shutdown as defined in
/etc/slim.conf
with
halt_cmd /sbin/poweroff
and
reboot_cmd /sbin/reboot
Will be performed and no login.