To elaborate on dalai's response:
- a build process based on a gitlab runner could fill the contents of gitlab pages by rendering HTML and/or PDF from the AsciiDoc of the repository
- the build could trigger once the content in the repository changes and refresh the gitlab pages
- from what I heard: gitlab pages can be access restricted with the same permissions mechanism as the repository
- a static site generator (jekyll, jbake, etc.) could provide a navigation if an AsciiDoc file or a static HTML file is not sufficient