UITextField within UIScrollView Constraint Resize

I am having issues with Constraints and setting up a simple UITextField within a UIScrollView. I have set the constraint to the left and right of the UITextField so that it should autoresize if I rotate from Portrait to Landscape. However if you embed this same constraint within a UIScrollView, the UIScrollView doesn't resize the UITextField but instead it gives you a horizontal scroll bar and the UITextField uses the default width. How can you not use width or minimum width?

How can I auto-resize the UITextField within a UIScrollView using the constraints? I'm just trying to setup a simple form within a UIScrollView but the sizing is not working.