public class CrossDomainCookie : IHttpModule

     {

         private string m_RootDomain = string.Empty;

         #region IHttpModule Members

         public void Dispose()

         {

         }

         public void Init(HttpApplication context)

         {

             m_RootDomain = ConfigurationManager.AppSettings["RootDomain"];

             Type stateServerSessionProvider = typeof(HttpSessionState).Assembly.GetType("System.Web.SessionState.OutOfProcSessionStateStore");

             FieldInfo uriField = stateServerSessionProvider.GetField("s_uribase", BindingFlags.Static | BindingFlags.NonPublic);

             if (uriField == null)

                 throw new ArgumentException("UriField was not found");

             uriField.SetValue(null, m_RootDomain);

             context.EndRequest += new System.EventHandler(context_EndRequest);

         }

         void context_EndRequest(object sender, System.EventArgs e)

         {

             HttpApplication app = sender as HttpApplication;

             for (int i = ; i < app.Context.Response.Cookies.Count; i++)

             {

                 app.Context.Response.Cookies[i].Domain = m_RootDomain;

             }

         }

         #endregion

     }

 <configuration>

   <appSettings>

     <add key="RootDomain" value=".session.com"/>

   </appSettings>

   <connectionStrings/>

   <system.web>

     <machineKey decryptionKey="FD69B2EB9A11E3063518F1932E314E4AA1577BF0B824F369" validationKey="5F32295C31223A362286DD5777916FCD0FD2A8EF882783FD3E29AB1FCDFE931F8FA45A8E468B7A40269E50A748778CBB8DB2262D44A86BBCEA96DCA46CBC05C3" validation="SHA1" decryption="Auto"/>

     <sessionState cookieless="false" timeout="" mode="StateServer" stateConnectionString="tcpip=127.0.0.1:42424"/>

     <httpModules>

       <add name="CrossDomainCookieModule" type="WebLibrary.CrossDomainCookie, WebLibrary"/>

     </httpModules>

     <pages controlRenderingCompatibilityVersion="3.5" clientIDMode="AutoID"/>

   </system.web>

   <!--

         The system.webServer section is required for running ASP.NET AJAX under Internet

         Information Services 7.0.  It is not necessary for previous version of IIS.

     -->

   <system.webServer>

     <modules>

       <add name="CrossDomainCookieModule" preCondition="managedHandler" type="WebLibrary.CrossDomainCookie, WebLibrary"/>

     </modules>

   </system.webServer>

 </configuration>