Facebook Tab Authentication

Question

Is it possible to authenticate a user from a tab app?

I am trying to create an ASP.NET MVC 3 facebook tab app that needs to be able to post to wall.

My first guess was using the CanvasAuthorizeAttribute

[CanvasAuthorize(Permissions="publish_stream")]

but it makes my tab redirect to the the login facebook authorization page and then back to the canvas page and not staying in the fanpage (tab).

Then I remove the CanvasAuthorize and tried the following

public string Index()
{
    bool isAuthorized = FacebookWebContext.Current.IsAuthorized("publish_stream");

    return isAuthorized.ToString();
}

from that I could decide to launch the authorize popup if the user is not authorized, but I am facing a problem here.

• Previously authorizing the app with stream_publish permission by other means and then, running the page as an app ( http://apps.facebook.com/myapp/mytab ) returns true while running the page from a fanpage tab ( http://www.facebook.com/myfanpage?sk=app_myappid ) returns false !

Why can't the tab read the permission but the canvas page can?

Answer 1

From you Facebook Page, you can detect whether the user has authorized your app or not by examining the signed_request. If user_id and oauth_token are passed, then the user has already authorized your app. If not, you can do something like this from your Controller Action:

    string[] extendedPermissions = new[] { "publish_stream", "manage_pages" };
    var oauth = new FacebookOAuthClient(FacebookWebContext.Current.Settings);
    var parameters = new Dictionary<string, object> {
                { "redirect_uri", "http://www.facebook.com/pages/{SomeFacebookPage}?sk=app_{appId}"}
            };

    parameters["scope"] = String.Join(",", extendedPermissions);
    var loginUrl = oauth.GetLoginUrl(parameters);

    return Redirect(loginUrl.AbsoluteUri);

After your user authenticates your app, the user will be sent to the "redirect_uri", which can be your app tab on a Facebook Page.