Question

I’m building an application that allows users to post message to their facebook from the application. To problem I’m having that I don’t know how to get the user access_token for the publish_stream permission.

This is what I’ve got so far:

        var fb = new FacebookClient();
        dynamic result = fb.GetLoginUrl(new
        {
            client_id = AppID,
            client_secret = AppSecret,
            grant_type = "client_credentials",
            scope = "publish_stream",
            state = "http://localhost:17578/Facebook.aspx",
            redirect_uri = "http://localhost:17578/Facebook.aspx"
        });

That works fine and it returns a ‘code’ in the querystring. However, I’m not sure what to do with that code.
The ‘old’ Facebook C# sdk contained the FacebookOAuthClient class which had the ExchangeCodeForAccessToken() method, but I don’t know what the replacement of this static method is in the new SDK.

So the question really is: How to exchange the code that is returned for an access_token?

Answer 1

After you get the code query string parameter you must make a call to the Facebook Graph API to get the access token.

https://developers.facebook.com/docs/howtos/login/server-side-login/

FacebookClient client = new FacebookClient();
dynamic result = client.Get("oauth/access_token", new { client_id = Settings.Social_Facebook_App_Id, client_secret = Settings.Social_Facebook_Secret_Key, code = Request.QueryString["code"], redirect_uri = Settings.Social_Facebook_Login_Redirect_URI });
if (result.error == null)
{
    Session["AccessToken"] = client.AccessToken = result.access_token;
    dynamic user = client.Get("me", new { fields = "name,username,email" });
    string userName = user.username;

    mu = Membership.GetUser(userName);
    if (mu == null)  // Register
    {
        RegisterModel rm = new RegisterModel();
        rm.Email = user.email;
        rm.UserName = userName;
        return View("Register", rm);
    }
    else
    {
        FormsAuthentication.SetAuthCookie(userName, true);
        return RedirectToAction(MVC.Home.Index());
    }
}