maintain such user on all web pages.

As the others have mentioned, use session variables. Do make sure when you are done with the user's session variable to delete it when finished. Otherwise, you will eventually (as this may take a very long time to have happen) run out of memory on the server where the values are kept.

The one step no-one else mentioned, is to create a new base page, which redirects to the login page if the user is not already logged in. From there, it just works.