The reason why local auth should not be used in many-faceted, but that doesn’t mean you have to use someone else. I host my own OIDC server for my services (which it itself also has a local login, or other auth to github, google, and a few others), that’s fine, but it should not be in the webapp itself, that’s not its job at the very basic.
Side topic, It’s interesting how much their new HTML-eex engine is copying even more of what Drab did years ago (though it looks like it’s missing some abilities that drab had like fast in-place identification and replacement for the live swaps)… Still irritated about all that… >.>