EWS Oauth异常：请求失败。 远程服务器返回错误：（401）未经授权

Question

I'm trying to create a bot that can book meetings. In order to do that i need to access the calendar of an employee to get FreeBusy info to ultimately book a meeting. I'm trying to avoid hardcoding the email and password and for that I want to use an access token from Azure AD to call EWS. I set the properties for

public static ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2013);

using this method:

       public static async System.Threading.Tasks.Task UseExchangeService(IDialogContext context, string userEmailAddress, SecureString     userPassword)
         {
        string authority = ConfigurationManager.AppSettings["authority"];
        string clientID = ConfigurationManager.AppSettings["clientID"];
         string resource = ConfigurationManager.AppSettings["resource"];
        string appKey = ConfigurationManager.AppSettings["appkey"];

        AuthenticationContext authenticationContext = new AuthenticationContext(authority, false);
        ClientCredential clientCred = new ClientCredential(clientID, appKey);
        AuthenticationResult authenticationResult = await authenticationContext.AcquireTokenAsync(resource, clientCred);
        service.Url = new Uri(ConfigurationManager.AppSettings["serverName"] + "/ews/exchange.asmx");
        service.TraceEnabled = true;
        service.TraceFlags = TraceFlags.All;
        service.Credentials = new OAuthCredentials(authenticationResult.AccessToken);


        // USING THIS LINE IT WORKS FINE!
        // service.Credentials = new NetworkCredential(userEmailAddress, userPassword); // VIRKER

    }

I do get the access token from Azure AD and I have granted the permission for the application in Azure AD.

I use this method to extract the freebusytimes, it contains other more code to display the times as buttons on a herocard, but this is the call to EWS:

       List<AttendeeInfo> attendees = new List<AttendeeInfo>();
        attendees.Add(new AttendeeInfo()
        {
            SmtpAddress = "MyEMAIL",
            AttendeeType = MeetingAttendeeType.Organizer
        });

        attendees.Add(new AttendeeInfo()
        {
            SmtpAddress = BookersEmail,
            AttendeeType = MeetingAttendeeType.Required
        });
        //DateTime date1 = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day.Ad, 7, 0, 0)
        // Specify options to request free/busy information and suggested meeting times.
        AvailabilityOptions availabilityOptions = new AvailabilityOptions();
        availabilityOptions.GoodSuggestionThreshold = 49;
        availabilityOptions.MaximumNonWorkHoursSuggestionsPerDay = 0;
        availabilityOptions.MaximumSuggestionsPerDay = 20;
        // Note that 60 minutes is the default value for MeetingDuration, but setting it explicitly for demonstration purposes.
        availabilityOptions.MeetingDuration = 60;
        availabilityOptions.MinimumSuggestionQuality = SuggestionQuality.Excellent;

        //TimeWindow hej = new TimeWindow();
        DateTime StartDay = DateTime.Now.AddDays(1);
        TimeSpan ts = new TimeSpan(9, 0, 0);
        DateTime StartTime = StartDay.Date + ts;

        availabilityOptions.DetailedSuggestionsWindow = new TimeWindow(StartTime, DateTime.Now.AddDays(4));
        availabilityOptions.RequestedFreeBusyView = FreeBusyViewType.FreeBusy;
        // Return free/busy information and a set of suggested meeting times. 
        // This method results in a GetUserAvailabilityRequest call to EWS.
        GetUserAvailabilityResults results = service.GetUserAvailability(attendees,
                                                                         availabilityOptions.DetailedSuggestionsWindow,
                                                                         AvailabilityData.FreeBusyAndSuggestions,
                                                                         availabilityOptions);

I have created the application in Azure AD and I have granted the following permissions: Office 365 Exchange Online:

Use Exchange Web Services with full access to all mailboxes

Read and write calendars in all mailboxes

Read and write user and shared calendars

Access mailboxes as the signed-in user via Exchange Web Services

I've tried other answers i found on stackoverflow, however they do not do the trick for me. Hope You can help

Answer 1

I am not familiar with EWS, however as far as I know that the Microsoft Graph also provide the similar feature for find the available meeting time using the rest below( refer here ):

POST /me/findMeetingTimes

And if you want to using this REST for the web application so that your web app can delegate the sign-in user to perform the operation for Exchange, we can use the OAuth 2.0 code grant flow . And for how to use this flow to integrate with Microsoft Graph, you can refer the links below:

Get started with Microsoft Graph in an ASP.NET 4.6 MVC app

And here is the detail for this flow:

Authorize access to web applications using OAuth 2.0 and Azure Active Directory

Hope it is helpful.