How to determine Session Timeout using when reusing CookieContainer

Question

I have the following code which re-uses a CookieContainer which logs in on the first request, but just uses the cookie container for requests after.

After a period of time if idle the site will give a Session Timeout, I will need to perform the login again.

Q: Can I determine (with the cookie container object) if the timeout has happened or is it best to determine if it has happened from the HttpWebResponse which happens to contains text like 'session timeout'. What is the best way to do this?

        private static CookieContainer _cookieContainer;
    private static CookieContainer CurrentCookieContainer
    {
        get
        {
            if (_cookieContainer == null || _cookieContainer.Count == 0)
            {
                lock (_lock)
                {
                    if (_cookieContainer == null || _cookieContainer.Count == 0)
                    {
                        //_cookieContainer.GetCookies(
                        _cookieContainer = DoLogin();
                    }
                }
            }

            return _cookieContainer;
        }
        set
        {
            _cookieContainer = value;
        }
    }

And then this method calls out to the container:

        public static string SomeMethod(SomeParams p)
        {
            HttpWebRequest request_thirdPartyEnquiryDetails = (HttpWebRequest)WebRequest.Create(thirdPartyEnquiryDetails);
            CookieContainer cookieContainer = CurrentCookieContainer;
            request_thirdPartyEnquiryDetails.CookieContainer = cookieContainer;
//... and it goes on to submit a search and return the response
        }

Answer 1

Well, since the timeout is 30 mins, I have set the login to repeat after 25 mins.

private static DateTime? lastLoggedIn;

    private static CookieContainer _cookieContainer;
    private static CookieContainer CurrentCookieContainer
    {
        get
        {
            if (_cookieContainer == null || _cookieContainer.Count == 0 || !lastLoggedIn.HasValue || lastLoggedIn.Value.AddMinutes(25) < DateTime.Now)
            {
                lock (_lock)
                {
                    if (_cookieContainer == null || _cookieContainer.Count == 0 || !lastLoggedIn.HasValue || lastLoggedIn.Value.AddMinutes(25) < DateTime.Now)
                    {
                        _cookieContainer = DoLogin();
                        lastLoggedIn = DateTime.Now;
                    }                        
                }
            }

            return _cookieContainer;
        }
        set
        {
            _cookieContainer = value;
        }
    }

As an extra precaution, I check the HttpResponse for the text which returns when the page session times out (although its now expected this won't be seen). If this happens I set the lastLoggedIn date to null and run the search method again.