Calculate remaining two points of rectangle from given two points

I want to draw a rectangle using THREE.shape. I have two points of the rectangle lets say (x1, y1) and (x2, y2). And its easy to get other two points which will be (x2, y1) and (x1, y2). But its only possible if we want to draw the plane parallel to x and y axis.
But how can I draw the rectangle if I rotate the camera along z axis by certain degrees and still want my rectangle to be perfectly aligned with my screen but rotated with respect to x and y axis.

You can put your points in a group that you will rotate, keeping the camera without rotation, and then get your points global coordinates for drawing the rectangle…

How are the points going to be specified?
Would it be something like a click and set interface?