Image Processing: Reshape an Oblique Rectangle to a Regular Rectangle

I am trying to take an image taken at any angle and reshape it to be a "Perfect" rectangle.

I have Threshold the image to binary so that it might be easier to work with.

I then also found the boundaries as well as a mask to remove the background from the paper.

My question is what would be the best way to reorient the rectangle to appear "straight vertical/horizontal"? Since I will be using different sets of images I'd preferably like to automate this process. I thought of finding the corners and then using those to somehow resize the image but am having a hard time finding them currently. Any help, such as tips or paths to follow, would be greatly appreciated.

Thanks