Draw Square in NDC space from two world points

I have two points in world coordinates. I want to draw a square in NDC space whose length is equal to the distance between these two points in NDC space.

Reason: I want to make sure that the aspect ratio of my scene is okay ot not. My camera is updating constantly along with one of these points. However the distance between these two points in world space seems constant, but the distance between them in NDC space seems changing.