QUESTION Site with public & private section

[jmstack]

I want to build a simple information site (read-only, no need for any user interaction)
Part of the website is to be public, i.e. readable for everyone.
The biggest part of the website will be "internal" and only be readable for a defined group of people.
(People living in our housing association)

There will be no "sensitive secrets" in the internal section, so simple security  will do.
I am thinking that internal users will just have to type in a (common for all internal users) password to be
allowed access to the internal section of the site.

Any suggestions on how to accomplish this with GS?
I have been trying various plugins, but not found a working solution...
Tia
/JohanS