Why app-only tokens doesn't work for beta API in Outlook Mail REST API?

Question

I'm trying to use beta version of MS Outlook Mail REST with app-only tokens but the requests doesn't work as expected.

For example, folder hierarchy synchronization behaves like v2.0 and doesn't work with app-only tokens.

Answer 1

The app-only token works well for this request. What's the error you get?

To call this request with app-only token, we need to specific user instead of me in the document like request below:

GET https://outlook.office365.com/api/v2.0/users/userPrincipalName/MailFolders

And to get the app-token, I use the code below:

   public static async Task<string> GetTokenByCert(string clientId, string tenant, string certThumbprint,string resource)
    {
        string authority = $"https://login.windows.net/{tenant}";

        X509Certificate2 cert = CertHelper.FindCert(certThumbprint);
        var certCred = new ClientAssertionCertificate(clientId, cert);
        var authContext = new Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContext(authority);
        AuthenticationResult result = null;
        try
        {
            result = await authContext.AcquireTokenAsync(resource, certCred);
        }
        catch (Exception ex)
        {
        }

        return result.AccessToken;
    }