Sessions in WordPress?

Question

WordPress

Good afternoon, such a situation has arisen, you need to close access to some pages and buttons of the site, the site is made on the WordPress engine. Access will be open only to those users who will enter a certain code that they will receive.
The question is how to close the page or button when the session is not running, and if the user has not entered the code, then a form pops up to enter the code.
Thank you.