会话变量在页面加载之间不会持久存在

Can someone tell me why the session vars are not passing between pages? They were working up to 2 days ago. Now its not? There is a third party system that logs users in based on the third party system. I direct users to the login page with the return url. The third party system logs a user in and passes their id and a token generated on their end and returns them to my site with the id and the token in the url.Can someone tell me why the session vars are no