Get access token to facebook page - WPF

Question

I am developing a WPF application that needs post on wall of a facebook\'s Page, and this without login window. Well, I want to get access token for my facebook page, and th

Answer 1

If you use the fb_exchange_token call, it will give you a token that expires after 60 days. In order to make it work correctly, I had to go through the login web flow to guarantee I got an up-to-date page access token.

1. Go to the Facebook App dashboard
2. If you haven't already added the Facebook Login product, click "+ Add Product" and select Facebook Login
3. Enable the "embedded browser control" option and enter https://www.facebook.com/connect/login_success.html as the allowed redirect URL.
4. Make a Window with a WebView control on it. The WebBrowser control no longer works; the browser engine powering it is too old.

5. Add code to listen for the navigation to the success URL:

   this.webView.NavigationCompleted += (sender, args) =>
   {
       if (args.Uri.AbsolutePath == "/connect/login_success.html")
       {
           if (args.Uri.Query.Contains("error"))
           {
               MessageBox.Show("Error logging in.");
           }
           else
           {
               string fragment = args.Uri.Fragment;
               var collection = HttpUtility.ParseQueryString(fragment.Substring(1));
               string token = collection["access_token"];
   
               // Save the token somewhere to give back to your code
           }
   
           this.Close();
       }
   };
   

6. Add code to navigate to the facebook login URL:

   string returnUrl = WebUtility.UrlEncode("https://www.facebook.com/connect/login_success.html");
   this.webView.Source = new Uri($"https://www.facebook.com/dialog/oauth?client_id={appId}&redirect_uri={returnUrl}&response_type=token%2Cgranted_scopes&scope=manage_pages&display=popup");
   

7. Call window.ShowDialog() to pop up the login window, then grab the user access token.

8. Create some models to help you out:

   public class AccountsResult
   {
       public List data { get; set; }
   }
   
   public class Account
   {
       public string access_token { get; set; }
   
       public string id { get; set; }
   }
   

9. Using the user access token, get the page access token:

   FacebookClient userFacebookClient = new FacebookClient(userAccessToken);
   var accountsResult = await userFacebookClient.GetTaskAsync("/me/accounts");
   string pageAccessToken = accountsResult.data.FirstOrDefault(account => account.id == PageId)?.access_token;
   
   if (pageAccessToken == null)
   {
       MessageBox.Show("Could not find page under user accounts.");
   }
   else
   {
       FacebookClient pageFacebookClient = new FacebookClient(pageAccessToken);
   
       // Use pageFacebookClient here
   }