planetarium - sun points to camera

I checked out source files of this demo: https://www.blend4web.com/en/demo/planetarium/
The Sun does not rotate with whole scene. It's location is somehow locked to the camera.
The question is, how is it made?
I need the same behaviour.

The Sun does not rotate with whole scene. It's location is somehow locked to the camera.
The question is, how is it made

You can use billboard option in the object setup to achvie that effect.

Thanks! Cool!