Docs Portal behind a login

[WriterAndrew]

Hi, all,
Slightly quirky request here, but...
The company I work for and another are merging.
All my docs are publically available, in HTML5, via a Flare-created docs portal.
The docs from the "other half" of the company are currently in PDF and that part of the product line (cybersecurity) has a mandate that all customer/user docs have to be secured behind a login. Currently, these PDFs are posted to the support portal which provides the login capabilities.
However, the other writer is keen to be able to move to topic-based documentation in the future, but the support site does not support being used as a Docs Portal.
So, my question is "Does anyone know an easy way to create a joint docs portal (with all content coming from Flare, regardless of the output) but to have an area of it that can only be accessed by logging in using a secure user authorization?"
Many thanks

[lorynj]

Configure your web server to require login?