I'd like to encourage you to take another look at Authentik, it sounds like their Proxy Provider is exactly what you're looking for: https://docs.goauthentik.io/docs/providers/proxy/

Authentik can certainly get complex, but only if you want/need it to. It is by far the most user-friendly IDP solution I've found, especially for what it offers. Their docs also have step-by-step guides for how to integrate a lot of popular self-hosted apps.

Only takes a couple mins to spin up a test environment using their Docker compose file: https://docs.goauthentik.io/docs/installation/docker-compose

Apps: SSO via Authentik where I can, unique user/pass combo via Bitwarden where I can't (or, more realistically, don't want to).

General infra: Unique RSA keys, sometimes Ed25519

Core infra: Yubikey

This is overkill for most, but I'm a systems engineer with a homelab, so it works well for me.

If you're wanting to practice good security hygiene, the bare minimum would be using unique cred pairs (or at least unique passwords) per app/service, auto-filled via a proper password manager with a browser extension (like KeePassXC or Bitwarden).

Edit: On the network side, if your goal is to just do some basic internal self-hosting, there's nothing wrong with keeping your topo mostly flat (with the exception of a separate VLAN for IoT, if applicable). Outside of that, making good use of firewalls will help you keep things pretty tight. The networking rabbit hole is a deep one, not always worth the dive unless you're truly wanting to learn for the sake of a cert/job/etc.

Thanks to The Primeagen, I've recently become fond of pronouncing it /skwiːl/

Y'know: Squeal, Squeal-lite, Pee-squeal, etc.

We're so tightly integrated with the M$ ecosystem at my work, it's painful. My department has even been going out of it's way to self host (F)OSS alternatives where we can, just to avoid as much of the cludge as possible.

Has anyone tried out the new Teams integration feature that Mattermost recently rolled out for Enterprise customers? If so, any good?

If we can seamlessly sync calls/meetings from Teams into Mattermost and ditch the Teams client for our day-to-day comms, I might have a fighting chance at convincing my supervisor to pivot my department.

If you ever reach a point where self-hosting does become a possibility, I'd recommend checking out Mattermost.