I've tried adding the following to my /etc/polkit-1/localauthority/50-local.d/
[storage group mount override]
Identity=unix-user:ada
Action=org.freedesktop.udisks2.filesystem-mount;org.freedesktop.udisks2.filesystem-mount-system
ResultsAny=yes
ResultsInactive=yes
ResultsActive=yes
As far as I can remember, it worked in Ubuntu 17.10. Now, I'm using Ubuntu 18.04(mini.iso) + i3wm without any Display Manager.
Update 1:
Tried adding the following lines to /etc/polkit-1/rules.d/10-udisks2.rules
polkit.addRule(function(action, subject) {
if ((action.id == "org.freedesktop.udisks2.filesystem-mount-system" ||
action.id == "org.freedesktop.udisks2.filesystem-mount") &&
subject.isInGroup("sudo")) {
return polkit.Result.YES;
}
});
still getting the password prompt when mounting drives in Thunar.