transformation - Detect transform from detection of QR code?

I want to calculate the transform I need to render a 3D object in my world.

How I see my idea:

• You open a camera


• You point it at a QR code


• The app detects the QR code and returns the 4 corners and the correct direction


• The app calculates the transform that this QR code is currently at (I need help with this step)


• The app uses that transform to render the 3D object in a fixed position over the QR code

I want something like Vuforia, but for QR codes (as they are used often).

I don't really know how I can extract the transform from the detected QR code (I will get the location of the 4 corners)