Image-Sorter/Image Sorter/AuthenticationHelper.cs

using Microsoft.Graph;
using Microsoft.Identity.Client;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;

namespace Image_Sorter
{
    public class AuthenticationHelper
    {
        // The Client ID is used by the application to uniquely identify itself to the v2.0 authentication endpoint.
        static string clientId = Program.MsaClientId;
        public static string[] Scopes = { "Files.Read.All" };
        public static IPublicClientApplication app = PublicClientApplicationBuilder.Create(clientId).WithRedirectUri("http://localhost:8192/oauth2callback/").Build();
        //public static PublicClientApplicationBuilder IdentityClientApp = PublicClientApplicationBuilder.Create(clientId);// new PublicClientApplication(clientId);

        public static string AccessToken = null;
        public static IAccount UserAccount = null;

        public static DateTimeOffset Expiration;

        private static GraphServiceClient graphClient = null;

        // Get an access token for the given context and resourceId. An attempt is first made to 
        // acquire the token silently. If that fails, then we try to acquire the token by prompting the user.
        public static GraphServiceClient GetAuthenticatedClient()
        {
            if (graphClient == null)
            {
                // Create Microsoft Graph client.
                try
                {
                    graphClient = new GraphServiceClient(
                        "https://graph.microsoft.com/v1.0",
                        new DelegateAuthenticationProvider(
                            async (requestMessage) =>
                            {
                                var token = await GetTokenForUserAsync();
                                requestMessage.Headers.Authorization = new AuthenticationHeaderValue("bearer", token);
                                // This header has been added to identify our sample in the Microsoft Graph service.  If extracting this code for your project please remove.
                                //requestMessage.Headers.Add("SampleID", "uwp-csharp-apibrowser-sample");

                            }));
                    return graphClient;
                }

                catch (Exception ex)
                {
                    Console.WriteLine("Could not create a graph client: " + ex.Message);
                }
            }

            return graphClient;
        }


        /// <summary>
        /// Get Token for User.
        /// </summary>
        /// <returns>Token for user.</returns>
        public static async Task<string> GetTokenForUserAsync()
        {
            AuthenticationResult authResult;
            /*try
            {
                authResult = await app.AcquireTokenInteractive(null).WithPrompt(Microsoft.Identity.Client.Prompt.SelectAccount).ExecuteAsync();
                AccessToken = authResult.AccessToken;
                UserAccount = authResult.Account;
            }

            catch (Exception e)
            {
                //Console.WriteLine(e);
            }*/
            // Attempt to aquire an existing token. If we're already authed, the existing account will be valid
            try
            {
                authResult = await app.AcquireTokenSilent(Scopes, UserAccount).ExecuteAsync();
                AccessToken = authResult.AccessToken;
                UserAccount = authResult.Account;
            }

            catch (Exception)
            {
                if (AccessToken == null || Expiration <= DateTimeOffset.UtcNow.AddMinutes(5))
                {
                    authResult = await app.AcquireTokenInteractive(null).WithPrompt(Microsoft.Identity.Client.Prompt.SelectAccount).ExecuteAsync();

                    AccessToken = authResult.AccessToken;
                    UserAccount = authResult.Account;
                    Expiration = authResult.ExpiresOn;
                }
            }

            return AccessToken;
        }
    }
}