SetCookie(), GetCookie(), DeleteCookie()

using System;
using System.Windows.Browser;

// Source: http://www.eggheadcafe.com/community/aspnet/12/10035916/retrieve-and-delete-cooki.aspx 
namespace CookiesDemo {

 public static class CookieExtensions {

 /// <summary>
 /// Sets a persistent cookie which expires after the given number of days
 /// </summary>
 /// <param name="doc">The HtmDocument to extend</param>
 /// <param name="key">the cookie key</param>
 /// <param name="value">the cookie value</param>
 /// <param name="days">The number of days before the cookie expires</param>
 public static void SetCookie(this HtmlDocument doc, string key, string value, int days) {
 DateTime expiration = DateTime.UtcNow + TimeSpan.FromDays(days);
 SetCookie(doc, key, value, expiration);
 }

 /// <summary>
 /// Sets a persistent cookie with an expiration date
 /// </summary>
 /// <param name="doc">The HtmDocument to extend</param>
 /// <param name="key">the cookie key</param>
 /// <param name="value">the cookie value</param>
 public static void SetCookie(this HtmlDocument doc, string key, string value, DateTime expiration) {
 string oldCookie = doc.GetProperty("cookie") as String;
 string cookie = String.Format("{0}={1};expires={2}", key, value, expiration.ToString("R"));
 doc.SetProperty("cookie", cookie);
 }

 /// <summary>
 /// Retrieves an existing cookie
 /// </summary>
 /// <param name="doc">The HtmDocument to extend</param>
 /// <param name="key">cookie key</param>
 /// <returns>null if the cookie does not exist, otherwise the cookie value</returns>
 public static string GetCookie(this HtmlDocument doc, string key) {
 string[] cookies = doc.Cookies.Split(';');
 key += '=';
 foreach (string cookie in cookies) {
 string cookieStr = cookie.Trim();
 if (cookieStr.StartsWith(key, StringComparison.OrdinalIgnoreCase)) {
 string[] vals = cookieStr.Split('=');

 if (vals.Length >= 2) {
 return vals[1];
 }

 return string.Empty;
 }
 }

 return null;
 }

 /// <summary>
 /// Deletes a specified cookie by setting its value to empty and expiration to -1 days
 /// </summary>
 /// <param name="doc">The HtmDocument to extend</param>
 /// <param name="key">the cookie key to delete</param>
 public static void DeleteCookie(this HtmlDocument doc, string key) {
 string oldCookie = doc.GetProperty("cookie") as String;
 DateTime expiration = DateTime.UtcNow - TimeSpan.FromDays(1);
 string cookie = String.Format("{0}=;expires={1}", key, expiration.ToString("R"));
 doc.SetProperty("cookie", cookie);
 }
 }
}

HtmlPage.Document.SetCookie("key", "example", 5);

string value = HtmlPage.Document.GetCookie("key");