@oborosaur Ultimately, even though the phrase "ambient authority" is well-known in some circles, I think the Principle of Least Authority (PoLA) is the more interesting concept to focus on.
PoLA is all about granularity. Ideally, don't grant monolithic access to anything, and don't grant any access to monolithic things. Build modular systems and grant fine-grained access to the modules that need it.
And handles are a really great tool for doing that. But not the only tool.