ASP.net C# Code Behind creating a Facebook login button

Facebook Login is a great way and very easy way for your user to connect to your website or to your client’s website. To make a Facebook Login button using ASP.net C# and only code behind calls you will need first to download the Facebook asp.net SDK, you can do so from the following link and add the Facebook.dll files as a reference in your project

• Add any button on the website and give it any image you want
• In the code behind add the following code to the on click event

string callbackUrl = “http://yourdomain.com/FacebookConnect.aspx”;
string appID = “yourFacebookAppID”;
//Request offline access and publish to the users stream access.
Responce.Redirect(” string.Format(“https://graph.facebook.com/oauth/authorize?client_id={0}&redirect_uri={1}&scope=offline_access,email,publish_stream”, appID, callbackUrl)”);

• After redirecting to facebook the user will give you the requested access in “SCOPE” and will redirect back to the mentioned URL with a QueryString CODE
• Inside FacebookConnect.aspx add the following code

using Facebook;
protected void Page_Load(object sender, EventArgs e)
{
     if (!string.IsNullOrEmpty(Request["code"]) && !Page.IsPostBack)
     {
           HandleFacebookCallback();
     }
     else
     {
           //Do something, the user didn't give you access;
     }
}
private void HandleFacebookCallback()
{
  var oauthResult = Request.Params["code"];
  string accessToken = GetOauthTokens(oauthResult)["access_token"].ToString();

  if (string.IsNullOrEmpty(accessToken))
  {
    // failed to get access token do something
  }
  var fb = new FacebookClient(accessToken);
  dynamic me = fb.Get("me");
  // get all the user information
  string email = me.email;
  string facebookID = me.id;
  byte[] imageBytes = webClient.DownloadData(string.Format("https://graph.facebook.com/{0}/picture", me.id));

  //perform login for the user
}

private Dictionary<string, string> GetOauthTokens(string code)
{
  Dictionary<string, string> tokens = new Dictionary<string, string>();
  string clientId = "facebook app ID"
  string redirectUrl = "http://yourdomain.com/FacebookConnect.aspx";
  string clientSecret = "FacebookAppSecret";
  string scope = "offline_access,email,publish_stream";
  string url = string.Format("https://graph.facebook.com/oauth/access_token? 
client_id={0}&redirect_uri={1}&client_secret={2}&code={3}&scope={4}",
 clientId, redirectUrl, clientSecret, code, scope);

  HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
  using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)
  {
    StreamReader reader = new StreamReader(response.GetResponseStream());
    string retVal = reader.ReadToEnd();
    foreach (string token in retVal.Split('&'))
    {
       tokens.Add(token.Substring(0, token.IndexOf("=")),
       token.Substring(token.IndexOf("=") + 1, token.Length - token.IndexOf("=") - 1));
    }
  }
  return tokens;
}

Using the code mentioned above you should be able to get the information of the use and to make him login. This code worked great on one of the websites i made. If you see any error please drop me a message in the comment section below.

Thank you for sharing 🙂