Interim Web Server / Web Service Implementation

We are looking for a developer that can implement an interim server between our app and another server. The main task of this interim server is to act in between these two. Our app will send a request to the interim server through RESTful API and the interim server will then connect to the other server (performing authentication). Finally, the interim server will take the information of the server to the mobile app. For the interim server we want to use [login to view URL] The authentication required is a 3 legged OAuth. We want to implement this server in two weeks time. Everything is already implemented apart from the interim server.