Changing the shape of a spotlight

Artistic Support Lighting and Rendering
1

Hi there, in Blender 2.7 there was an option to make a spotlight square. How can I do this in Blender 2.8?

Thanks!

2

I just happened to see a video by CGMatter explaining exactly that today:
1:36 to 2:24 covers this.

You would need a square/rectangular image mask to do this, or possibly make a node-based one.