Comment 6 for bug 932598

Robert, there is currently no special code to handle /var/lib/lightdm/.Xauthority, it's handled by the same code as for any other user session. Would it be possible to make a special case there, so that the greeter uses /run/lightdm/.Xauthority, and every other user session uses ~/.Xauthority, as usual?

If not, we could think about shipping a /var/lib/lightdm/.Xauthority -> /run/lightdm/.Xauthority symlink.

In either case, either lightdm itself or the upstart job needs to create /run/lightdm/ at startup with the right permissions.