据说下面的这段代码这件可以实现不同域之间的session共享：

namespace CSASPNETShareSessionBetweenSubDomainsModule
{
    /// <summary>
    /// A HttpModule used for sharing the session between Applications in
    /// sub domains.
    /// </summary>
    public class SharedSessionModule : IHttpModule
    {
        // Cache settings on memory.
        protected static string applicationName = ConfigurationManager.AppSettings["ApplicationName"];
        protected static string rootDomain = ConfigurationManager.AppSettings["RootDomain"];

#region IHttpModule Members
        /// <summary>
        /// Initializes a module and prepares it to handle requests.
        /// </summary>
        /// <param name="context">
        /// An System.Web.HttpApplication
        /// that provides access to the methods,
        /// properties, and events common to all application objects within
        /// an ASP.NET application.
        /// </param>
        public void Init(HttpApplication context)
        {
            // This module requires both Application Name and Root Domain to work.
            if (string.IsNullOrEmpty(applicationName) ||
                string.IsNullOrEmpty(rootDomain))
            {
                return;
            }

// Change the Application Name in runtime.
            FieldInfo runtimeInfo = typeof(HttpRuntime).GetField("_theRuntime",
                BindingFlags.Static | BindingFlags.NonPublic);
            HttpRuntime theRuntime = (HttpRuntime)runtimeInfo.GetValue(null);
            FieldInfo appNameInfo = typeof(HttpRuntime).GetField("_appDomainAppId",
                BindingFlags.Instance | BindingFlags.NonPublic);

appNameInfo.SetValue(theRuntime, applicationName);

// Subscribe Events.
            context.PostRequestHandlerExecute += new EventHandler(context_PostRequestHandlerExecute);
        }

/// <summary>
        /// Disposes of the resources (other than memory) used by the module
        /// that implements.
        /// </summary>
        public void Dispose()
        {
        }
        #endregion

/// <summary>
        /// Before sending response content to client, change the Cookie to Root Domain
        /// and store current Session Id.
        /// </summary>
        /// <param name="sender">
        /// An instance of System.Web.HttpApplication that provides access to
        /// the methods, properties, and events common to all application
        /// objects within an ASP.NET application.
        /// </param>
        void context_PostRequestHandlerExecute(object sender, EventArgs e)
        {
            HttpApplication context = (HttpApplication)sender;

// ASP.NET store a Session Id in cookie to specify current Session.
            HttpCookie cookie = context.Response.Cookies["ASP.NET_SessionId"];

if (context.Session != null &&
                !string.IsNullOrEmpty(context.Session.SessionID))
            {
                // Need to store current Session Id during every request.
                cookie.Value = context.Session.SessionID;

// All Applications use one root domain to store this Cookie
                // So that it can be shared.
                if (rootDomain != "localhost")
                {
                    cookie.Domain = rootDomain;
                }

// All Virtual Applications and Folders share this Cookie too.
                cookie.Path = "/";
            }
        }
    }
}

两个项目分别引用一个这个类，就用实现跨域之间的session共享。