//add a single cookie to cookies, if already exist, update its value
    public void addCookieToCookies(Cookie toAdd, ref CookieCollection cookies, bool overwriteDomain)
    {
        bool found = false;

        if (cookies.Count > 0)
        {
            foreach (Cookie originalCookie in cookies)
            {
                if (originalCookie.Name == toAdd.Name)
                {
                    // !!! for different domain, cookie is not same,
                    // so should not set the cookie value here while their domains is not same
                    // only if it explictly need overwrite domain
                    if ((originalCookie.Domain == toAdd.Domain) ||
                        ((originalCookie.Domain != toAdd.Domain) && overwriteDomain))
                    {
                        //here can not force convert CookieCollection to HttpCookieCollection,
                        //then use .remove to remove this cookie then add
                        // so no good way to copy all field value
                        originalCookie.Value = toAdd.Value;

                        originalCookie.Domain = toAdd.Domain;

                        originalCookie.Expires = toAdd.Expires;
                        originalCookie.Version = toAdd.Version;
                        originalCookie.Path = toAdd.Path;

                        //following fields seems should not change
                        //originalCookie.HttpOnly = toAdd.HttpOnly;
                        //originalCookie.Secure = toAdd.Secure;

                        found = true;
                        break;
                    }
                }
            }
        }

        if (!found)
        {
            if (toAdd.Domain != "")
            {
                // if add the null domain, will lead to follow req.CookieContainer.Add(cookies) failed !!!
                cookies.Add(toAdd);
            }
        }

    }//addCookieToCookies

    //add singel cookie to cookies, default no overwrite domain
    public void addCookieToCookies(Cookie toAdd, ref CookieCollection cookies)
    {
        addCookieToCookies(toAdd, ref cookies, false);
    }

    

    //ref CookieCollection localCookies
    foreach (Cookie newCookie in cookiesToUpdate)
    {
        if (isContainCookie(newCookie, omitUpdateCookies))
        {
            // need omit process this
        }
        else
        {
            addCookieToCookies(newCookie, ref localCookies);
        }
    }