exchange code for token facebook-c#-sdk

Question

I am using The Facebook-C#-Sdk v5.0.3 to create a non-canvas webforms app in vb.net and i am having trouble exchanging the returned facebook code for the access_token. Does anyone have an example (C# or vb.net) that I can look at?

Thanks awesome Stackoverflow community!

Answer 1

Try this:

var app = new FacebookClient(FacebookContext.Current.AppId, FacebookContext.Current.AppSecret);
var accessToken = app.AccessToken

or this:

var app = new FacebookClient(new Authorizer().Session.AccessToken);
var accessToken = app.AccessToken

Answer 2

You can use the appId and appSecret as the app accesstoken.

For instance you can do this when debugging an user token to see if it's valid

            var client = new FacebookClient();
            dynamic result = client.Get("debug_token", new
            {
                input_token = user.AccessToken,
                access_token = string.Format("{0}|{1}", appId, appSecret)
            });

Later you can check result.data.is_valid to see if the user token is still valid.

If you need the access_token of a user, you first need to set the scope correctly, later you can do this:

    if (Request["code"] == null)
                    {
                        Response.Redirect(string.Format(
                            "https://graph.facebook.com/oauth/authorize?client_id={0}&redirect_uri={1}&scope={2}",
                            appId, Request.Url.AbsoluteUri, scope));
                    }
                    else
                    {
                        var tokens = new Dictionary<string, string>();

                        string url =
                            string.Format(
                                "https://graph.facebook.com/oauth/access_token?client_id={0}&redirect_uri={1}&scope={2}&code={3}&client_secret={4}",
                                appId, Request.Url.AbsoluteUri, scope, Request["code"], appSecret);

                        var request = WebRequest.Create(url) as HttpWebRequest;

                        using (var response = request.GetResponse() as HttpWebResponse)
                        {
                            var reader = new StreamReader(response.GetResponseStream());

                            string vals = reader.ReadToEnd();

                            foreach (string token in vals.Split('&'))
                            {
                                tokens.Add(token.Substring(0, token.IndexOf("=")),
                                    token.Substring(token.IndexOf("=") + 1, token.Length - token.IndexOf("=") - 1));
                            }
                        }

                        // Get access token from tokens
                        var accessToken = tokens["access_token"];

                    }

This will redirect the user to Facebook asking for permission. Then Facebook will return to the return URL with code in the querystring, use that code to retreive the user's access_token.

Keep in mind this will be a short-lived access_token, you will probably have to expand it.