sending link in e-mail

hi all,

how should I send a url link in an e-mail, given that any access directly to the url will re-direct to the login page?

When clicking on the link, the user will be re-directed to the login page.
After submitting the credentials, the user will go to the home page ... how do I make it so that he/she will be re-directed to the url in the e-mail?

Note:
The re-direction to the login page is due to the fact that all pages implement a master page that has this code in the Load_Page:

public partialclassadminMasterPage : System.Web.UI.MasterPage
{
             protectedvoid Page_Load(object sender, EventArgs e)
             {
                //check the session cookie
                //if it expired or the user tried to access this page directly, redirect to userLogin.aspx
                if (!Request.IsAuthenticated)
                {
                    Response.Redirect("~/userLogin.aspx");
                }
             }
}

Thanks,

kowalsky