While many of the uses of Jupyter are solely for educating others, there are instances where the information being accessed is and should remain confidential. Jupyter allows you to put up barriers to entry to your notebook in several manners.

When we identify the user, we are authenticating that user. This is normally done by presenting a login challenge before allowing entry, where the user has to enter a username and password.

If the instance of Jupyter hosting, your notebook is installed on a web server and you can use the web server's access control to limit access to your notebook. Further, most of the vendors that support notebook hosting provide a mechanism to limit access to specific users.