Facebook

using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

/*
     * Creator: Dialog
     *
     * Contact:
     * E-mail: Relekka(at)outlook .com
     * XMPP: [email protected]
     *
     * Created: 09.22.2014
     */

namespace ConsoleApplication1
{
    /// <summary>
    /// Validates Facebook credentials
    /// </summary>
    public static class Facebook
    {
        private static HttpClient _client;

        /// <summary>
        /// Asynchronously tries to sign in to Facebook
        /// </summary>
        /// <param name="creds">The credentials to sign in to. Enter an e-mail address for the username</param>
        /// <returns>A boolean indicating success. False if something went wrong or the credentials are invalid</returns>
        public static async Task<bool> TrySignInAsync(NetworkCredential creds)
        {
            const string signInUrl = "https://www.facebook.com/login.php?login_attempt=1";
            var tokens = await GetTokenAsync();

            using (var message = new HttpRequestMessage(HttpMethod.Post, new Uri(signInUrl)))
            {
                message.Content = new FormUrlEncodedContent(new Dictionary<string, string>
                {
                    { "lsd", tokens.Item1 },
                    { "email", creds.UserName },
                    { "pass", creds.Password },
                    { "default_persistent", "0" },
                    { "timezone", "-120" },
                    { "lgnrnd", tokens.Item2 },
                    { "lgnjs", UnixTime().ToString() },
                    { "locale", "nl_NL" }
                });
                message.Content.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");

                var response = await _client.SendAsync(message);
                var responseContent = await response.Content.ReadAsStringAsync();

                return responseContent.IndexOf("<input class=\"uiLinkButtonInput\"", StringComparison.Ordinal) != -1;
            }
        }

        /// <summary>
        /// Asynchronously gets Facebook's authenticity tokens
        /// </summary>
        /// <returns>A tuple with the lsd token as its first item, and lgnrnd as its second</returns>
        private static async Task<Tuple<string, string>> GetTokenAsync()
        {
            _client = new HttpClient(new HttpClientHandler() { CookieContainer = new CookieContainer() }, true);
            _client.DefaultRequestHeaders.UserAgent.ParseAdd("Mozilla/5.0 (Windows NT 6.1; WOW64; rv:32.0) Gecko/20100101 Firefox/32.0");

            var pageSource = await _client.GetStringAsync(new Uri("https://facebook.com"));
            return ParseTokens(pageSource);
        }

        /// <summary>
        /// Parses Facebook tokens from a page source
        /// </summary>
        private static Tuple<string, string> ParseTokens(string pageSource)
        {
            const string lsdPattern = "(\\[\"LSD\",\\[\\]).*?(\"token\").*?(\".*?\")";
            const string lgnrndPattern = ".*?(\"lgnrnd\").*?(value).*?(\".*?\")";

            var lsdMatch = Regex.Match(pageSource, lsdPattern);
            var lgnrndMatch = Regex.Match(pageSource, lgnrndPattern);

            if (!(lsdMatch.Success && lgnrndMatch.Success))
            {
                throw new WebException("Could not get tokens.");
            }

            var trimChars = new[] { '\\', '"' };
            var lsdToken = lsdMatch.Groups[3].Value.Trim(trimChars);
            var lgnrndToken = lgnrndMatch.Groups[3].Value.Trim(trimChars);

            var result = new Tuple<string, string>(lsdToken, lgnrndToken);
            return result;
        }

        /// <summary>
        /// Gets the unix epoch time
        /// Credits: Ben Cull @ stackoverflow.com
        /// </summary>
        /// <returns>Unix epoch time in seconds</returns>
        private static long UnixTime()
        {
            var epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
            return Convert.ToInt64((DateTime.Now.ToUniversalTime() - epoch).TotalSeconds);
        }
    }
}