I’m dying for like a full 100% deep dive on secure, modern web authentication and authorized, with matching code examples, just because I’m so curious about the subject.

The best I’ve done so far is to read some open source Oauth code like fosite- but this still doesn’t cover user authentication, or key signing best practices, or secret management or (all the other things I don’t know about but could contribute to an insecure implementation).

I feel like I’m at best getting 10% of the picture.

With that as a foundation you'll still only know enough to get yourself into trouble, but you'll have the vocabulary and background to be able to find more tailored resources, to immediately reject a lot of articles and guides, to form your own opinions about lists if best practices, and to continue learning via hands-on experience.

The underlying assumption is that there are nuggets of wisdom here and there which mostly add up to the knowledge you're looking for, but that they aren't all in the same place and that they're buried under a deluge of inapplicable, SEO'd garbage. I think that's a decent model for thinking about Docker, but other topics like learning most mainstream spoken languages might have more dedicated resources which will serve you better.