PowerBI Rest API C# throwing 'Operation returned an invalid status code 'Unauthorized''

Hey all,

I've been following some tutorials and am trying to access some reports from our Power BI instance. I can successfully authenticate and get a Bearer Auth token, but when using my PowerBIClient to try to communicate I get an Unauthorized error. 

Can someone tell me if what I am doing is wrong?

Any help to point me in the right direction would be awesome, thank you!

        public async Task<string> GetToken()
        {
            //The client id that Azure AD created when you registered your client app.
            try
            {
                System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

                List<string> scopes = new List<string>();
                scopes.Add("https://analysis.windows.net/powerbi/api/.default");

                var confidentialClient = ConfidentialClientApplicationBuilder
                           .Create("{my app ID from Azure"")
                           .WithClientSecret("{my client secret from azure}")
                           .WithAuthority(new Uri("https://login.microsoftonline.com/{my azure tenant ID}"))
                           .WithRedirectUri("https://localhost:44300/")
                           .Build();

                var accessTokenRequest = confidentialClient.AcquireTokenForClient(scopes);
                var authResult = await accessTokenRequest.ExecuteAsync();

                return authResult.AccessToken;
            }
            catch
            {
                throw;
            }
        }

        private async Task Authenticate()
        {
            if (_currentAccessToken == null)
            {
                var tokenCredentials = new TokenCredentials(await GetToken(), "Bearer");

                client = new PowerBIClient(new Uri("https://api.powerbi.com/"), tokenCredentials);

                _currentAccessToken = tokenCredentials;
            }
        }

public async Task<string> PostExportRequest(Guid reportId, Guid groupId, FileFormat format, IList<string> pageNames = null, string urlFilter = null)
        {
            try
            {
                var exportRequest = new ExportReportRequest
                {
                    Format = format
                };

                if(_currentAccessToken == null) 
                    await Authenticate();
                //also fails
                var groups = await client.Groups.GetGroupsAsync();
                //fails with unauthorized
                var export = await client.Reports.ExportToFileInGroupAsync(reportId, groupId, exportRequest);

                // Save the export ID, you'll need it for polling and getting the exported file
                return export.Id;
            }
            catch
            {
                throw;
            }
        }