facebook-c#-sdk Windows Phone 7 Authentication - Why the secret? - facebook

Question

This post { AppSecret with Windows Phone 7 }
indicates that the WP7 sample doesn't use the AppSecret to login from windows phone, but the current sample in the 5.3.2 download does use the secret.
However, FacebookOAuthClient.cs throws exceptions if it isn't provided. Also, http://blog.prabir.me/post/Facebook-CSharp-SDK-Writing-your-first-Facebook-Application.aspx
shows a sample without using the AppSecret.
Reading Facebooks developer docs it appears that the secret is intended for backend (webserver) auth to facebook, not client apps, and that it is poor practice, maybe insecure, and probably fattening to include your secret in your client application.
Do I misunderstand the guidance, or is there some way to authenticate with the facebook-c#-sdk without using the secret?
Thanks!

Answer 1

In WP 7.0 there was a problem with Fragment in Url (all after # was truncated). Facebook return auth token in Url Fragment, so without it it was impossible to authentificate like desktop/mobile app. The solution was to switch to Web mode, where you can receive auth token if you know AppSecret, so it was the only solution for that (but with security gaps).
In WP 7.1 Fragment Url bug was closed and now you can use normal authentification mode (without AppSecret on client).

Answer 2

If you could access anything of mine WITHOUT first having me authorize the app (solely using the app ID without an access token or a app secret), then that would be a HUGE security hole. Not only to my profile, but to any app out there since the app id is public.
The short answer is, you are required to have a user (or other type of) access token or an app secret to get information.

Answer 3

I figured out the problem was not with the SDK, but the Windows Phone 7 sample included. That sample uses the server-side flow. The changes necessary to the example were:
changing:
loginParameters["response_type"] = "code";
to:
loginParameters["response_type"] = "token";
and removing the entire labda function in webBrowser1_Navigated:
...
// The url is the result of OAuth 2.0 authentication.
if (oauthResult.IsSuccess)
{
var oauthClient = new FacebookOAuthClient { AppId = AppId, AppSecret = AppSecret };
// we got the code here
var code = oauthResult.Code;
oauthClient.ExchangeCodeForAccessTokenCompleted +=
(o, args) =>
{
...
and replaced it with this:
if (_fLoginMode && oauthResult.IsSuccess && !string.IsNullOrEmpty(oauthResult.AccessToken))
{
Dispatcher.BeginInvoke(() => NavigationService.Navigate(new Uri("/FacebookInfoPage.xaml?access_token=" + oauthResult.AccessToken, UriKind.Relative)));
}
And, of course removing the AppSecret constant