401 Unauthorized when subscribing to push notifications using the Exchange service and OAuth

Question

I am trying to access the EWS managed API (subscribe to push notifications) using oauth as shown below:

var authenticationTask = await authenticationContext.AcquireTokenAsync("https://outlook.office365.com", new ClientCredential(clientID, clientSecret));
string targetSmtp = "[e-mail]";
ExchangeService exchangeService = new ExchangeService(ExchangeVersion.Exchange2013);
exchangeService.Url = someURL;
exchangeService.TraceEnabled = true;
exchangeService.TraceFlags = TraceFlags.All;
exchangeService.ImpersonatedUserId = new ImpersonatedUserId(ConnectingIdType.PrincipalName, "[e-mail]");
exchangeService.HttpHeaders.Add("X-AnchorMailbox", targetSmtp);
exchangeService.Credentials = new OAuthCredentials(authenticationTask.AccessToken);
PushSubscription subscription = exchangeService.SubscribeToPushNotifications(
                                            new[] { someFolder },
                                            new Uri(postBackUrl),
                                            15,
                                            null,
                                            EventType.NewMail,
                                            EventType.Created,
                                            EventType.Deleted,
                                            EventType.Modified,
                                            EventType.Moved,
                                            EventType.Copied);

I can get a token for my application, but when I subscribe a user ( [e-mail] ) to push notifications, I get an "The request failed. The remote server returned an error: (401) Unauthorized."error

Update: I tried to follow exactly the same step mentioned here: Azure AD-only access tokens to impersonate Exchange, but still receive 401.

Ashish

Answer 1

, , , ( , ). , , .: https://blogs.msdn.microsoft.com/exchangedev/2015/01/21/building-daemon-or-service-apps-with-office-365-mail-calendar-and-contacts-apis-oauth2-client-credential-flow/