Small Sample .NET App

We have a simple REST+XML API that just take 4 GET parameters and sends an XML response. A new potential partner has asked us to build a small sample App to show them how to consume it. UI has one small window with 2 text boxes, one button and one text field. User fills in the two text boxes and presses the button labelled "Check". App constructs the url, connects to our API and displays the result in the text field with Green or Red for Allow/Reject. The url looks like this: [login to view URL] The auth is a simple algorithm. We will share a better description with the winner, but this is a really simple task. It is very important that the call to our API is wrapped in a function that accepts the payload and attraction_id parameters so that our new partner can just use that function in their code. We will work with one milestone and as per Freelancer terms it will only be released after we have received the working sample and it's source.