Recently I've been getting asked a great deal about how to perform non-interactive authentication with the Dynamics 365 WebApi in a server to server authentication scenario. The most common scenario is that you have an external server application that needs to access the Dynamics 365 WebApi.
The good news is that it's easy using Application Users. Here is a short video showing you how.
The code in the video is as follows:
public static async Task Auth()
string api = "https://org.crm11.dynamics.com/api/data/v9.0";
AuthenticationParameters ap = AuthenticationParameters.CreateFromResourceUrlAsync(
var creds = new ClientCredential("ApplicationID", "ClientSecret");
AuthenticationContext authContext = new AuthenticationContext(ap.Authority);
var token = authContext.AcquireTokenAsync(ap.Resource, creds).Result.AccessToken;
using (HttpClient httpClient = new HttpClient())
httpClient.Timeout = new TimeSpan(0, 2, 0);
new AuthenticationHeaderValue("Bearer", token);
HttpResponseMessage response = await httpClient.GetAsync(api + "/contacts?$top=1");
Hope this helps!