PolicyKit not applying with systemd on Debian Jessie

[Sam Nazarko <email@samnazarko.co.uk>]

​I am trying to allow a non-root user to mount disks on a Debian Jessie (minbase debootstrap) system. I am using systemd (installed systemd and systemd-sysv) packages and trying to achieve disk automounting via policykit and udisks.

I installed: udisks, udisks-glue and policykit-1. I created a systemd script for udisks-glue. 

I then, using pkaction, determined I need to authorise:

org.freedesktop.udisks.filesystem-mount

So I created /var/lib/polkit-1/localauthority/90-mandatory.d/diskmount.pkla

[mountdisks]
Identity=unix-user:testuser
Action=org.freedesktop.udisks.filesystem-mount
ResultActive=yes

Running udisks-glue as root will mount the device under /media without issue; however, running udisks-glue as testuser will tell me I am not authorised. 

I have verified that I installed udisks1, and even changing Action=org.freedesktop.udisks.filesystem-mount to Action=* is still not authorising this user to mount disks on the fly. 

My debootstrap did not bring in consolekit, and as far as I can tell, I shouldn't need this. 

How do I best diagnose why PolicyKit is seemingly ignoring my PKLA?