LoginAsync.cs

public async Task<bool> LoginAsync()
{
    	var authenticator = new Windows.Security.Authentication.OnlineId.OnlineIdAuthenticator();
	var mobileServicesTicket = new Windows.Security.Authentication.OnlineId.OnlineIdServiceTicketRequest("https://yourendpoint.azure-mobile.net/", "JWT");

	var ticketRequests = new List<OnlineIdServiceTicketRequest>() { mobileServicesTicket };

	var authResult = await authenticator.AuthenticateUserAsync(ticketRequests, CredentialPromptType.PromptIfNeeded);

	if ((authResult.Tickets.Count == 1) && (authResult.Tickets[0].ErrorCode == 0))
	{                            
		var accessToken = authResult.Tickets[0];          
		var res = await _mobileServiceClient.LoginWithMicrosoftAccountAsync(accessToken.Value);

		return true;
	}
	else
	{            
		return false;
	}
}