I am attempting to prove out Constant Contact as a mass email solution for an application programmed in C# with the .Net framework. So far, I have been able to demonstrate all necessary functionality for authorization, contact list syncing, and email creation/sending in Postman. All of the API calls work perfect. However, once I attempted to implement the server flow authorization programmatically I ran into an issue of not receiving the JSON response content containing the auth token/refresh token. I receive an HttpResponseMessage with a 200 status, but it doesn't contain the tokens as expected.
Can you provide a demo using System.Net.Http.HttpClient to create a post request to get the auth and refresh tokens?