Using SPUserToken for Adding a list Item

I have a scenario where users with no permissions on a list be able to add items/modify items on the list. I am trying to use SpUserToken to achieve this but the list item is either created using system account or the user is denied access, Whereas I need the actual user in the created column. Thanks in Advance.

Access Denied While Item Update:-

        protected void ImpersonationDemo()
        {
            // This could be inside SPSecurity.RunWithElevatedPrivileges
            // if you need to raise permissions initially
            using (SPSite site = new SPSite(config.strUrl))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    #region Get LoggedIn User
                    SPUser spUser = web.CurrentUser;
                    #endregion
                    // Add a new list item by User 1
                    Impersonate(strUserName, web);
                }
            }
        }

        protected void Impersonate(string LoginID, SPWeb Web)
        {
            // Get User Token for the user we are trying to impersonate
            SPUserToken token = Web.AllUsers["i:"+ LoginID].UserToken;
            

            // IMPORTANT - Open a new site using this token
            using (SPSite site = new SPSite(config.strUrl, token))
            {
                using (SPWeb w = site.OpenWeb())
                {
                    SPList Announcement = w.Lists["Help Form List"];
                    SPListItem Item = Announcement.AddItem();
                    Item["Title"] = "Test";
                    Item.Update();
                }
            }
        }

Item Created as System Account :-

private void usrtokentest()
        {
            SPUserToken systemAccountUserToken = SPContext.Current.Site.SystemAccount.UserToken;
            using (SPSite elevatedSite = new SPSite(config.strUrl, systemAccountUserToken)) 
            {
                using (SPWeb w = elevatedSite.OpenWeb())
                {
                    w.AllowUnsafeUpdates = true;
                    SPList Announcement = w.Lists["Announcement List"];
                    SPListItem Item = Announcement.AddItem();
                    Item["Title"] = "Test";
                    Item.Update();
                    w.AllowUnsafeUpdates = false;
                }
 
            }
        }