Authenticating routes

### Have you read the Contributing Guidelines on issues?

- [X] I have read the [Contributing Guidelines on issues](https://github.com/facebook/docusaurus/blob/main/CONTRIBUTING.md#reporting-new-issues).

### Description

Suppose I am having authentication in place, how do I protect my navbar routes or markdown files routes?
I can't understand how to approach towards it in docusaurus.

### Self-service

- [ ] I'd be willing to address this documentation request myself.