Creating User Authentication section of Contentful + Gatsby site

I have a Community site built with Contentful & Gatsby that is currently public. We would like to set up login sections of the site for our partners and their specific documentation. How do I set up users for specific sections of the site? We are talking read-only access, but to everything under a specific root. Different users will have different sections they can access, including our internal folks, who should be able to access everything. I can find information for login to contentful, information for creating authentication to gatsby using router that doesn’t seem to be leveraged similarly with Contentful, but not for a site created with contentful and gatsby. Any pointers appreciated.