Facebook api – Authentication – Xamarin.Forms, Azure Mobile Apps

I’ve got a Xamarin.Forms app (iOS, Android, UWP) connected to Azure Mobile Apps’ authentication service. From what I read, it seemed pretty straightforward to implement. I’m testing in a UWP project, and Android, both get the same result.

When logging in, I get this lovely “can’t connect to the service you need right now.” I don’t see anything wrong in my code. What might be going on here?

Windows UWP:

public async Task<bool> Authenticate()
{
    string message = string.Empty;
    var success = false;

    try
    {
        // Sign in with Facebook login using a server-managed flow.
        if (user == null)
        {
            user = await TaskService.DefaultService.CurrentClient.LoginAsync(MobileServiceAuthenticationProvider.Facebook);
            if (user != null)
            {
                success = true;
                message = string.Format("You are now signed-in as {0}.", user.UserId);
            }
        }

    }
    catch (Exception ex)
    {
        message = string.Format("Authentication Failed: {0}", ex.Message);
    }

    // Display the success or failure message.
    await new MessageDialog(message, "Sign-in result").ShowAsync();

    return success;
}

Android:

public async Task<bool> Authenticate()
{
    var success = false;
    var message = string.Empty;
    try
    {
        // Sign in with Facebook login using a server-managed flow.
        user = await TaskService.DefaultService.CurrentClient.LoginAsync(this,
            MobileServiceAuthenticationProvider.Facebook);
        if (user != null)
        {
            message = string.Format("you are now signed-in as {0}.",
                user.UserId);
            success = true;
        }
    }
    catch (Exception ex)
    {
        message = ex.Message;
    }

    // Display the success or failure message.
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.SetMessage(message);
    builder.SetTitle("Sign-in result");
    builder.Create().Show();

    return success;
}

Can’t connect to service error:

The settings on Facebook for the app:

Visited:

• https://azure.microsoft.com/en-us/documentation/articles/app-service-mobile-xamarin-forms-get-started-users/
• https://azure.microsoft.com/en-us/documentation/articles/app-service-mobile-how-to-configure-facebook-authentication/
• https://developer.xamarin.com/guides/xamarin-forms/web-services/authentication/azure/

EDIT:
I’ve tried moving the client code to App.cs:

private static MobileServiceClient _Client;
public static MobileServiceClient Client
{
    get
    {
        if(_Client == null) _Client = new MobileServiceClient(AppConstants.AzureMobileServiceURL);
        return _Client;
    }
    set { _Client = value; }
}

And the new call in MainPage.xaml.cs:

uesr = await Slated.App.Client.LoginAsync(MobileServiceAuthenticationProvider.Facebook);

Same result!

Another note: My Azure Mobile Services URL does include https://

EDIT 2:
Code below for logging on backend, looks to be an issue when redirecting to /login/facebook, the rest of the authentication appears to proceed OK. FYI – replaced the sensitive data with ____

2016-07-29T18:38:43  PID[6684] Verbose     Received request: GET https://________.azurewebsites.net/login/facebook
2016-07-29T18:38:43  PID[6684] Information Redirecting: https://www.facebook.com/dialog/oauth?response_type=code&client_id=_____________&redirect_uri=https%3A%2F%2F________.azurewebsites.net%2F.auth%2Flogin%2Ffacebook%2Fcallback&scope=public_profile&state=_____________________________&display=popup
2016-07-29T18:38:50  PID[6684] Verbose     Received request: GET https://________.azurewebsites.net/.auth/login/facebook/callback?code=____________________
2016-07-29T18:38:50  PID[6684] Verbose     Calling into external HTTP endpoint GET https://graph.facebook.com/oauth/access_token.
2016-07-29T18:38:51  PID[6684] Verbose     Calling into external HTTP endpoint GET https://graph.facebook.com/oauth/access_token.
2016-07-29T18:38:51  PID[6684] Verbose     Calling into external HTTP endpoint GET https://graph.facebook.com/me.
2016-07-29T18:38:51  PID[6684] Information Login completed for 'Thomas Gardner'. Provider: 'facebook'.
2016-07-29T18:38:51  PID[6684] Verbose     Writing 'AppServiceAuthSession' cookie for site '________.azurewebsites.net'. Length: 512.
2016-07-29T18:38:51  PID[6684] Information Redirecting: https://________.azurewebsites.net/login/facebook
2016-07-29T18:38:51  PID[6684] Verbose     Received request: GET https://________.azurewebsites.net/login/facebook
2016-07-29T18:38:51  PID[6684] Verbose     Found 'AppServiceAuthSession' cookie for site '________.azurewebsites.net'. Length: 512.
2016-07-29T18:38:51  PID[6684] Verbose     Authenticated Thomas Gardner successfully using 'Session Cookie' authentication.
2016-07-29T18:38:52  PID[6684] Verbose     Received request: GET https://________.azurewebsites.net/login/facebook
2016-07-29T18:38:52  PID[6684] Verbose     Found 'AppServiceAuthSession' cookie for site '________.azurewebsites.net'. Length: 512.
2016-07-29T18:38:52  PID[6684] Verbose     Authenticated __________ successfully using 'Session Cookie' authentication.
2016-07-29T18:38:52  PID[6684] Information Request, Method=GET, Url=https://________.azurewebsites.net/login/facebook, Message='https://________.azurewebsites.net/login/facebook'
2016-07-29T18:38:52  PID[6684] Information Message='Will use same 'JsonMediaTypeFormatter' formatter', Operation=JsonMediaTypeFormatter.GetPerRequestFormatterInstance
2016-07-29T18:38:52  PID[6684] Information Message='Selected formatter='JsonMediaTypeFormatter', content-type='application/json; charset=utf-8'', Operation=DefaultContentNegotiator.Negotiate
2016-07-29T18:38:52  PID[6684] Information Response, Status=404 (NotFound), Method=GET, Url=https://________.azurewebsites.net/login/facebook, Message='Content-type='application/json; charset=utf-8', content-length=unknown'

Backend Code: It is copied from MSFT’s template code. Not much has been done to the startup.
Startup.Mobile.App.cs

public partial class Startup
{
    public static void ConfigureMobileApp(IAppBuilder app)
    {
        HttpConfiguration config = new HttpConfiguration();

        //For more information on Web API tracing, see http://go.microsoft.com/fwlink/?LinkId=620686 
        config.EnableSystemDiagnosticsTracing();

        new MobileAppConfiguration()
            .UseDefaultConfiguration()
            .ApplyTo(config);

        // Use Entity Framework Code First to create database tables based on your DbContext
        Database.SetInitializer(new SlatedInitializer());

        // To prevent Entity Framework from modifying your database schema, use a null database initializer
        // Database.SetInitializer<SlatedContext>(null);

        MobileAppSettingsDictionary settings = config.GetMobileAppSettingsProvider().GetMobileAppSettings();

        if (string.IsNullOrEmpty(settings.HostName))
        {
            // This middleware is intended to be used locally for debugging. By default, HostName will
            // only have a value when running in an App Service application.
            app.UseAppServiceAuthentication(new AppServiceAuthenticationOptions
            {
                SigningKey = ConfigurationManager.AppSettings["SigningKey"],
                ValidAudiences = new[] { ConfigurationManager.AppSettings["ValidAudience"] },
                ValidIssuers = new[] { ConfigurationManager.AppSettings["ValidIssuer"] },
                TokenHandler = config.GetAppServiceTokenHandler()
            });
        }
        app.UseWebApi(config);
    }
}

public class SlatedInitializer : CreateDatabaseIfNotExists<SlatedContext>
{
    protected override void Seed(SlatedContext context)
    {
        /*List<Tasks> todoItems = new List<Tasks>
        {
            new Tasks { Id = Guid.NewGuid().ToString(), Text = "First item", Complete = false },
            new Tasks { Id = Guid.NewGuid().ToString(), Text = "Second item", Complete = false },
        };

        foreach (Tasks todoItem in todoItems)
        {
            context.Set<Tasks>().Add(todoItem);
        }*/

        base.Seed(context);
    }
}