First code snippet from blog post on free SMS

free_sms_1.cs

// Copyright (c) 2007, Jonas Follesø
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//     * Neither the name of the Jonas Follesø nor the
//       names of its contributors may be used to endorse or promote products
//       derived from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY Jonas Follesø ``AS IS'' AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL Jonas Follesø BE LIABLE FOR ANY
// DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

using System;
using System.IO;
using System.Net;
using System.Text;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Security.Authentication;

namespace Ung1881
{
    /// <summary>
    /// Proxy class wrapping the Ung1881 site for free SMS messaging.
    /// </summary>
    public class Ung1881Proxy
    {
        /// <summary>
        /// Variable used to store the authentication cookie.
        /// </summary>
        private CookieContainer cookies;

        /// <summary>
        /// Variable used to store the base uri of the page.
        /// </summary>
        private string baseUri = "https://www.ung1881.no/";

        /// <summary>
        /// Default constructor.
        /// </summary>
        public Ung1881Proxy()
        {
            cookies = new CookieContainer();
        }

        /// <summary>
        /// Login on Ung1881 using username and password.
        /// Authenticates against the site and keeps the auth cookie for next request.
        /// </summary>
        /// <param name="username">Username used to logon.</param>
        /// <param name="password">Password used to logon.</param>
        public void Login(string username, string password)
        {
            //Validate arguments.
            if (username == null || username.Length == 0)
                throw new ArgumentException("You must provide a username!", "username");

            if (password == null || password.Length == 0)
                throw new ArgumentException("You must provide a password!", "password");
            
            string loginUri = baseUri + "default____3.aspx";

            // Perform the first http request against the asp.net application login site.
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(loginUri);

            // Get the response object, so that we may get the session cookie.
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            // Populate the cookie container.
            request.CookieContainer = cookies;
            response.Cookies = request.CookieContainer.GetCookies(request.RequestUri);            

            // Read the incoming stream containing the login dialog page.
            StreamReader reader = new StreamReader(response.GetResponseStream());
            string loginDlgPage = reader.ReadToEnd();
            reader.Close();            

            // Extract the viewstate value from the login dialog page. 
            // We need to post this back, along with the username and password
            string viewState = GetViewState(loginDlgPage);

            // Build postback string.
            // This string will vary depending on the page. The best way to find out what your postback 
            // should look like is to monitor a normal login using a utility like Fiddler.
            string postback = String.Format("__VIEWSTATE={0}&defaultframework:login:tbxUsername={1}" +
                                            "&defaultframework:login:tbxPassword={2}" + 
                                            "&defaultframework:login:LoginButton.x=0&defaultframework:login:LoginButton.y=0",
                                            viewState, username, password);


            // Our second request is the POST of the username / password data.
            request = (HttpWebRequest)WebRequest.Create(loginUri);
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.CookieContainer = cookies;            

            // Write our postback data into the request stream
            StreamWriter writer = new StreamWriter(request.GetRequestStream());
            writer.Write(postback);
            writer.Close();

            reader = new StreamReader(request.GetResponse().GetResponseStream());
            loginDlgPage = reader.ReadToEnd();
            reader.Close();

            int index = loginDlgPage.IndexOf("Logg ut", StringComparison.OrdinalIgnoreCase);

            if (!CheckAuthenticationCookies() || index == -1)
            {
                throw new AuthenticationException("Unable to authenticate user. Check your username and password.");
            }            
        }

        /// <summary>
        /// Method sending a new SMS message trough Ung1881.
        /// </summary>
        /// <param name="phoneNumber">The phone number of the receiver.</param>
        /// <param name="message">The message to send.</param>
        /// <returns>True if the message was sendt sucsessfully.</returns>
        public void SendSms(string phoneNumber, string message)
        {
            //Validate arguments
            if (phoneNumber == null || phoneNumber.Length == 0)
                throw new ArgumentException("You need to provide a phone number!");

            if (message == null || message.Length == 0)
                throw new ArgumentException("You need to provide a message!");

            //Check that we have an authentication cookie.
            if (!CheckAuthenticationCookies())
                throw new AuthenticationException("User not authenticated. Call Login first!");

            //our third request is for the actual webpage after the login. 
            string smsUrl = baseUri + "/Templates/SMS____24.aspx";
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(smsUrl);
            request.CookieContainer = cookies;

            //and read the response
            StreamReader reader = new StreamReader(request.GetResponse().GetResponseStream());
            string page = reader.ReadToEnd();
            string viewState = GetViewState(page);

            string postback = String.Format("__VIEWSTATE={0}&defaultframework:_ctl2:Smssend:txtPhonenumber={1}" +
                                            "&defaultframework:_ctl2:Smssend:txtText={2}&defaultframework:_ctl2:Smssend:butSend.x=0" +
                                            "&defaultframework:_ctl2:Smssend:butSend.y=0", viewState, phoneNumber, message);

            reader.Close();

            request = (HttpWebRequest)WebRequest.Create(smsUrl);
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.CookieContainer = cookies;

            //Write our postback data into the request stream
            StreamWriter writer = new StreamWriter(request.GetRequestStream());
            writer.Write(postback);
            writer.Close();

            //Execute the request and read the response.
            reader = new StreamReader(request.GetResponse().GetResponseStream());
            page = reader.ReadToEnd();
            reader.Close();

            //Verify that the message was sent.
            if (!page.Contains("SMS sendt"))
            {
                throw new Ung1881Exception("Unable to send SMS message. Unknown error.");
            }            
        }

        /// <summary>
        /// Check if the user is authenticated.
        /// </summary>
        /// <returns>True if the user is authenticated.</returns>
        private bool CheckAuthenticationCookies()
        {
            bool authenticated = false;

            //Check that we have cookies.
            if (cookies != null)
            {
                //Check all cookies for the EpiServerLogin cookie.
                foreach (Cookie cookie in cookies.GetCookies(new Uri(baseUri)))
                {
                    if (cookie.Name != null && 
                        cookie.Name.Equals(".EPiServerLogin", StringComparison.OrdinalIgnoreCase))
                        authenticated = true;
                }
            }
            return authenticated;
        }

        /// <summary>
        /// Extract the viewstate data from a page.
        /// </summary>
        /// <param name="aspxPage">The raw HTML of the page.</param>
        /// <returns>Thew viewstate data of the page.</returns>
        private string GetViewState(string aspxPage)
        {
            Regex regex = new Regex("(?<=(__viewstate\".value.\")).*(?=\"./>)", RegexOptions.IgnoreCase);
            Match match = regex.Match(aspxPage);
            return System.Web.HttpUtility.UrlEncode(match.Value);
        }
    }
}