Link cookie to proper domain by referencing web.config & Save

[dba123]

I need to "tie together the cookie with the domain" by referencing the
information from my web.config below in my login's codebhind. I don't
understand how. I need to also save that after doing so:

<add key="cookieDoma inName" value=".test.co m" />

<authenticati on mode="Forms">
<forms loginUrl="login .aspx" name="CH.COM.AU TH" path="/"/>
</authentication>

something like this:
HttpContext.Cur rent.Applicatio n.GetKey(cookie DomainName);
then tie the cookie to the form name?

Here's the skeleton of our login.aspx.cs:

public partial class login : Web.BasePage
{
protected void Login1_LoggedIn (object sender, EventArgs e)
{
Login login = (Login)LoginVie w1.FindControl( "Login1");

CMembershipUser user =
(CMembershipUse r)Membership.Ge tUser(login.Use rName);
ProfileCommon profile = Profile.GetProf ile(login.UserN ame);
profile.User.CU serID = user.CUserID.To String();
profile.Save();

HttpContext.Cur rent.Applicatio n.GetKey(cookie DomainName); <<---my
attempt here to start relating the cookie to the domain...this is probably
incorrect.
}

}

I'm completely lost. I know this is simple but I haven't done much with
cookies in .NET 2.0. We are using the membership api in 2.0
--
dba123