API Call with code and token

Hi, I need to include in my project an OAUTH Authentication - API call to third party API. I need to pass a key and redirect uri. In return the API sends back a code (within the url). This code will then need to be taken and post another call (to the same API) with the token to get access to the entire functionality. More info about the third party API you can see here [login to view URL] The API will need to call through WEB Proxy API since CORS wont allow to get the response from the server. I am using MVC c# as the back end. I need to have this thing to integrate in my project. Fairly simple to an advance professional c# developer. This is prove of concept that I need to show to my client. If successful, then it will be an extension to the project.