using Microsoft.Graph; using System.Net.Http.Headers; namespace WebApp.Outlook { public class SDKHelper { // Get an authenticated Microsoft Graph Service client. public static GraphServiceClient AuthenticatedClient { get { var graphClient = new GraphServiceClient( new DelegateAuthenticationProvider( async (requestMessage) => { var accessToken = await AuthProvider.AuthProvider.Instance.GetAccessTokenAsync(); // Append the access token to the request. requestMessage.Headers.Authorization = new AuthenticationHeaderValue("bearer", accessToken); })); return graphClient; } } } }