Need more detailed documentation

Problem/Motivation

I'm using the latest D8 and D10 module versions. Setting up the module was complicate.
When trying to use it to authenticate users in a pure PHP code with the same credentials as my D8 or D10, I really don't know how to proceed.

• Are there texts, videos... documentations with examples?
• Is there some help to code no-drupal protected files? The callback file?
• Is possible to protect a bunch of files with only a generic Drupal setup and the same PHP code in the no-drupal website?