Get calendar schedules with Graph API from C# service

Question

I need to use the Microsoft Graph API to get free/busy schedules from the calendar with a .NET Core Windows service. According to Microsoft's own documentation I should use the following:

GraphServiceClient graphClient = new GraphServiceClient( authProvider );

var schedules = new List<String>()
{
    "[email protected]",
    "[email protected]"
};

var startTime = new DateTimeTimeZone
{
    DateTime = "2019-03-15T09:00:00",
    TimeZone = "Pacific Standard Time"
};

var endTime = new DateTimeTimeZone
{
    DateTime = "2019-03-15T18:00:00",
    TimeZone = "Pacific Standard Time"
};

var availabilityViewInterval = 60;

await graphClient.Me.Calendar
    .GetSchedule(schedules,endTime,startTime,availabilityViewInterval)
    .Request()
    .Header("Prefer","outlook.timezone=\"Pacific Standard Time\"")
    .PostAsync();

I have registered a new application using the Azure portal and given it the permission Calendars.Read.

My C# code:

try
{
    IConfidentialClientApplication clientApplication = ConfidentialClientApplicationBuilder
        .Create(_clientId)
        .WithTenantId(_tenantId)
        .WithClientSecret(_clientSecret)
        .Build();

    var authProvider = new ClientCredentialProvider(clientApplication);
    var graphClient = new GraphServiceClient(authProvider);

    var schedules = new List<string>
    {
        "[email protected]" // not actual mail used in my application
    };

    var startTime = new DateTimeTimeZone
    {
        DateTime = "2020-04-18T00:00:00",
        TimeZone = "Europe/Paris"
    };

    var endTime = new DateTimeTimeZone
    {
        DateTime = "2020-04-25T23:59:59",
        TimeZone = "Europe/Paris"
    };

    ICalendarGetScheduleCollectionPage scheduleList = await graphClient.Me.Calendar
        .GetSchedule(schedules, endTime, startTime, 60)
        .Request()
        .PostAsync().ConfigureAwait(false);
    Console.WriteLine("scheduleList.Count: " + scheduleList.ToList().Count);
}
catch (Exception ex)
{
    Console.WriteLine(ex.Message);
}

When I run my application I get the following exception:

Code: BadRequest

Message: Current authenticated context is not valid for this request. This occurs when a request is made to an endpoint that requires user sign-in. For example, /me requires a signed-in user. Acquire a token on behalf of a user to make requests to these endpoints. Use the OAuth 2.0 authorization code flow for mobile and native apps and the OAuth 2.0 implicit flow for single-page web apps.

Allen Wu Allen Wu · Accepted Answer · 2020-04-22T09:33:36

You are using Client credentials provider to create the authProvider.

However, Client credentials only works for app-only permissions.

But in your code graphClient.Me.Calendar means you are trying to get "my calendar", saying that the calendar of the signed-in user.

But there is no signed-in user because Client credentials is app-only.

So you need to implement Authorization code provider if you have a signed-in user. Then you can use graphClient.Me.Calendar to get the calendar.

Or if you don't have a signed-in user, you should keep using Client credentials provider and modify the code as: graphClient.Users["objectId of the user"].Calendar.

Get calendar schedules with Graph API from C# service

1 Answers