$ cat foo.sh
#! /bin/bash
id -a
# not just gksu-polkit id -a because gksu-polkit tries to interpret the -a
# this prompts for user's password only
$ gksu-polkit /home/user/foo.sh
uid=0(root) gid=0(root) groups=0(root) context=system_u:system_r:initrc_t:s0