When I installed davfs2, a dialog box said that it needed to be setuid to allow non-root users to mount a davfs file system. Moreover, mount.davfs also needs an entry in /etc/fstab, otherwise one gets an error "no entry for ... found in /etc/fstab". It should be fixed to make these things unneeded. As a comparison, sshfs doesn't need all that. I don't see what could be different between sshfs and davfs2 concerning permissions (e.g. both are based on FUSE).