I’m reopening this bug because it is very similar to my issue. When using my Macbook’s keyboard XF86MonBrightnessUp/Down keys to adjust screen brightness (probably on non-Macbooks too) in GDM or MATE, I am asked to enter my authentication password to make gnome-settings-daemon’s libexec/gsd-backlight-helper (or some equivalent program on MATE) change screen brightness.
This should not be so; gsd-backlight-helper should have PolicyKit, pam or setuid or whatever. Regards, Florian
