public async Task LogInAsync(Activity context)
{
if (!await IsLoggedInAsync(context))
{
var auth = new OAuth2Authenticator(
clientId: Service.ClientId,
scope: Service.Scope,
authorizeUrl: new Uri("https://m.facebook.com/dialog/oauth/"),
redirectUrl: new Uri("http://www.facebook.com/connect/login_success.html"));
var userAccount = await context.LoginAsync(auth);
Service.SaveAccount(context.BaseContext, userAccount);
}
}