OAuthWebSecurity.RegisterClient(new FacebookScopedClient("your_app_id", "your_app_secret"), "Facebook", null);

using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using System.Web;

    public class FacebookScopedClient : IAuthenticationClient
        {
            private string appId;
            private string appSecret;

            private const string baseUrl = "https://www.facebook.com/dialog/oauth?client_id=";
            public const string graphApiToken = "https://graph.facebook.com/oauth/access_token?";
            public const string graphApiMe = "https://graph.facebook.com/me?";


            private static string GetHTML(string URL)
            {
                string connectionString = URL;

                try
                {
                    System.Net.HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create(connectionString);
                    myRequest.Credentials = CredentialCache.DefaultCredentials;
                    //// Get the response
                    WebResponse webResponse = myRequest.GetResponse();
                    Stream respStream = webResponse.GetResponseStream();
                    ////
                    StreamReader ioStream = new StreamReader(respStream);
                    string pageContent = ioStream.ReadToEnd();
                    //// Close streams
                    ioStream.Close();
                    respStream.Close();
                    return pageContent;
                }
                catch (Exception)
                {
                }
                return null;
            }

            private  IDictionary<string, string> GetUserData(string accessCode, string redirectURI)
            {

                string token = GetHTML(graphApiToken + "client_id=" + appId + "&redirect_uri=" + HttpUtility.UrlEncode(redirectURI) + "&client_secret=" + appSecret + "&code=" + accessCode);
                if (token == null || token == "")
                {
                    return null;
                }
                string data = GetHTML(graphApiMe + "fields=id,name,email,username,gender,link&access_token=" + token.Substring("access_token=", "&"));

                // this dictionary must contains
                Dictionary<string, string> userData = JsonConvert.DeserializeObject<Dictionary<string, string>>(data);
                return userData;
            }

            public FacebookScopedClient(string appId, string appSecret)
            {
                this.appId = appId;
                this.appSecret = appSecret;
            }

            public string ProviderName
            {
                get { return "Facebook"; }
            }

            public void RequestAuthentication(System.Web.HttpContextBase context, Uri returnUrl)
            {
                string url = baseUrl + appId + "&redirect_uri=" + HttpUtility.UrlEncode(returnUrl.ToString()) + "&scope=email";
                context.Response.Redirect(url);
            }

            public AuthenticationResult VerifyAuthentication(System.Web.HttpContextBase context)
            {
                string code = context.Request.QueryString["code"];

                string rawUrl = context.Request.Url.OriginalString;
                //From this we need to remove code portion
                rawUrl = Regex.Replace(rawUrl, "&code=[^&]*", "");

                IDictionary<string, string> userData = GetUserData(code, rawUrl);

                if (userData == null)
                    return new AuthenticationResult(false, ProviderName, null, null, null);

                string id = userData["id"];
                string username = userData["username"];
                userData.Remove("id");
                userData.Remove("username");

                AuthenticationResult result = new AuthenticationResult(true, ProviderName, id, username, userData);
                return result;
            }
        }

public ActionResult ExternalLoginCallback(string returnUrl)

public static class String
    {
        public static string Substring(this string str, string StartString, string EndString)
        {
            if (str.Contains(StartString))
            {
                int iStart = str.IndexOf(StartString) + StartString.Length;
                int iEnd = str.IndexOf(EndString, iStart);
                return str.Substring(iStart, (iEnd - iStart));
            }
            return null;
        }
    }