Align billboard with Light direction

Godot Version

4.7

Question

I’m trying to figure out how to align a quad mesh to the sun direction of my scene, while making it always look at the camera (like a billboard). I’m trying to use this to create a godray/light shaft effect for my game.

I’m being heavily inspired by this reddit post and by t3ssel8r’s effect.

I’m still very very new to shader coding, so I would appreciate any help.