Bulk editing images to make squares for Instagram.

I have 2k rectangular images. I want to make them squares for Instagram. I can't crop them or distort them otherwise it'll remove the meaning. I need to add "letterboxes". Basically a color or white padding above and below the box until it's an exact square. Every rectangle is longer on the horizontal end.

Obviously I don't want to do this manually. Is there a way to automate this? How can I bulk edit these in the manner I described?