Redirect specific page with session o others way

Hi guys,
I put a label in menu called ‘Private’ that allow to insert name and password. If user data is correct the user will redirect in a page. For each user exist one page.
Now the problem is this:
If a user have a page with url: ‘example.com/heyjude’ and somebody go to ‘example.com/heyjude’ it is visible to all…
Fist all I thought to SESSION, but WordPress don’t accept SESSION so I read this https://silvermapleweb.com/using-the-php-session-in-wordpress/.
When I used session with php only i used to do:
1- session_start();
2- $_SESSION[‘username’] = $username;
then in a page ‘receive.php’
1-session_start();
2-$username = $_SESSION[‘username’];
But in WordPress how i can do it? Pages is dinamic and don’t exist a file .php for each page.

Alternatively, there are other way for my problem?

Sorry for bad english, thanks.