Page viewed with multiple passwords?

I don’t even know if this is possible.

I have been setting up a WordPress website for a large organization.

The website is to be viewed by the general public.

However, my client wants some pages or posts to be visible only by a staff member when they type in their “username and password” – I am assuming this is the username and password that they use to get on to their computers at their desks.

I know how to set up a post or page so that it is password protected. But in this case, there will be multiple passwords (I’m not sure how many, perhaps over 100).

Is it even possible to do this? If so, how. (You don’t have to tell me that just password protecting the page or post the normal way is the simpler and better way; I already know that. I think the client might want to save staff the “agony” of having to learn a new password.)