Mount a disk as user, read only
Note: ext4 (and other linux file systems) are mounted when honoring the files permissions, so one can't probably write to the root of the disk but *can* write in any folder belonging to him (same UID)
udisksctl mount --block-device /dev/sdaX --options ro
I even can use /dev/disk/by-label/xxxx as it will probably always be the same source (to various targets)
loop iso image
udisksctl loop-setup -r -f openSUSE-Leap-42.1-DVD-x86_64.iso
Option "-r" is to mount read only, omit it to have rw.
udisksctl mount -b /dev/loop0p1
Notice that udiskctl use "unmount" and not "umount"
udisksctl unmount -b /dev/loop0p1 udisksctl loop-delete -b /dev/loop0