gistfile1.cs

public static string PostWithAuth(string url, string requestBody = null, string method = "POST") {
  		using (WebClient client = new WebClient()) {
				var credentials = Convert.ToBase64String(Encoding.Default.GetBytes(APIKey));
				client.Headers.Add(HttpRequestHeader.Authorization, credentials);
				client.Headers.Add(HttpRequestHeader.ContentType, "application/json");//x-www-form-urlencoded
				if (!String.IsNullOrEmpty(requestBody))
					return client.UploadString(url, method, requestBody);
				else
					return client.UploadString(url, method);
			}
		}