var authCookie = FormsAuthentication.GetAuthCookie(userName,rememberUser.Checked);
// Get the FormsAuthenticationTicket out of the encrypted cookie
var ticket = FormsAuthentication.Decrypt(authCookie.Value);
// Create a new FormsAuthenticationTicket that includes our custom User Data
var newTicket = new FormsAuthenticationTicket(ticket.Version,ticket.Name,ticket.IssueDate,ticket.Expiration,ticket.IsPersistent,"userData");
// Update the authCookie's Value to use the encrypted version of newTicket
authCookie.Value = FormsAuthentication.Encrypt(newTicket);
// Manually add the authCookie to the Cookies collection
Response.Cookies.Add(authCookie);
FormsAuthentication.RedirectFromLoginPage(userName,rememberUser.Checked);

以下是我尝试访问它的方法：

if (HttpContext.Current.Request.IsAuthenticated )
{
    var authCookie = HttpContext.Current.Request.Cookies[FormsAuthentication.FormsCookieName];
    if (authCookie != null)
    {
        var authTicket = FormsAuthentication.Decrypt(authCookie.Value);
        string data = authTicket.UserData;
        // data is empty !!!
    }
}