为什么我的表单验证票证过期这么快?

FormsAuthenticationTicket 在一年内到期,但实际上在一小时左右到期。我不明白为什么。

以下是登录过程中涉及的所有代码:

public static bool Login(int id)
{
    try
    {
        string securityToken = UserHelper.AuthenticateUser(id);

        DateTime expiryDate = DateTime.Now.AddYears(1);
        FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(
             1, id.ToString(), DateTime.Now, expiryDate, true,
             securityToken, FormsAuthentication.FormsCookiePath);

        string encryptedTicket = FormsAuthentication.Encrypt(ticket);
        HttpCookie cookie = new HttpCookie(FormsAuthentication.FormsCookieName, encryptedTicket);
        cookie.Expires = expiryDate;

        HttpContext.Current.Response.Cookies.Add(cookie);

        return true;
    }
    catch
    {
        return false;
    }
}

<system.web>
    <machineKey validationKey="AutoGenerate"
    decryptionKey="AutoGenerate" validation="SHA1" />
    <compilation debug="true">
    <authentication mode="Forms">
        <forms loginUrl="~/Login.aspx" timeout="2880"/>
    </authentication>
...

我的方法有问题吗?为什么它会这么快过期?

编辑

protected void Application_AuthenticateRequest(object sender, EventArgs e)
{
    if (Request.PhysicalPath.EndsWith(".aspx") || Request.PhysicalPath.EndsWith(".axd") || Request.PhysicalPath.EndsWith(".ashx"))
        SecurityManager.SetPrincipal();
}

设置主体代码:

public static void SetPrincipal()
{
    ILivrePrincipal principal = null;
    FormsIdentity identity;
    UrlParameters urlParameters = UrlParametersHelper.GetUrlParameters(HttpContext.Current.Request);

    if (HttpContext.Current.Request.IsAuthenticated)
    {
        identity = (FormsIdentity)HttpContext.Current.User.Identity;

        User userProfile;
        urlParameters.SecurityToken = (((FormsIdentity)identity).Ticket).UserData;
        try
        {
            userProfile = UserHelper.GetUser(urlParameters.SecurityToken);
            UserHelper.UpdateLastActiveOn(userProfile);
            principal = new AuthenticatedPrincipal(identity, userProfile);
        }
        catch
        {
            //TODO: Log an exception
            FormsAuthentication.SignOut();
            principal = new AnonymousPrincipal(new GuestIdentity(), UserHelper.GetUser(null));
        }
    }
    else
    {
        principal = new AnonymousPrincipal(new GuestIdentity(), UserHelper.GetUser(null));
    }

    HttpContext.Current.User = principal;
}