Having gotten themselves on a good trajectory, our intrepid team now focuses more on the guts of the problem. In this episode they build the request that will eventually be sent to the API. Bit by bit they assemble the URL and the arguments that will be pumped into the Smarty Streets API.

I want you to notice how diligently they maintain the separation of concerns. They keep the construction of the address separate from the construction of the URL and authentication, which they keep separate from the HTTP protocol. Indeed, that separation, using the Decorator pattern, is the primary driver of the design of the Verifier.