Brian,

Did you try setting the cookie domain in your Forms Authentication info in the web.config on your umbraco instance?  You should have a forms authentication setting assuming the default similar to this...

    <authentication mode="Forms">
      <forms name="yourAuthCookie" loginUrl="login.aspx" protection="All" path="/" />
    </authentication>

Using your domain.com example you could change it to this:

    <authentication mode="Forms">
      <forms name="yourAuthCookie" loginUrl="login.aspx" protection="All" path="/" domain="domain.com" />
    </authentication>

Of course you would add the appropriate values for the other fields rather than use the default.

Thanks! I ended up using an HttpModule like this:

public class AppCookie : IHttpModule
{
    public AppCookie()
        {
    }

    public String ModuleName
    {
        get { return "AppCookie"; }
    }

    private HttpApplication _app = null;

    // In the Init function, register for HttpApplication
    // events by adding your handlers.
    public void Init(HttpApplication application)
    {
        application.PreRequestHandlerExecute +=
            (new EventHandler(this.Application_PreRequestHandlerExecute));
        _app = application;
    }

    private void Application_PreRequestHandlerExecute(Object source, EventArgs e)
    {
        if (HttpContext.Current.Session != null)
        {
            HttpCookie net_SessionId = _app.Response.Cookies["ASP.NET_SessionId"];

            if (net_SessionId == null)
            {
                net_SessionId = new HttpCookie("ASP.NET_SessionId");
            }

            net_SessionId.Value = _app.Session.SessionID;
            net_SessionId.Domain = "." + System.Configuration.ConfigurationSettings.AppSettings["CMSAppUrl"].ToString();
        }
    }

    public void Dispose()
    {
    }
}

And registering it in Umbraco's web.config:

<add name="AppCookie" type="AppCookie" />

And that did the trick. It was similar to the method used in the other app, so I wanted to stay consistent.

Oops, forgot to code format it!

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