Look into Single Sign-On services (SSO) like Authelia, Authentik, or KeyCloak. Most SSO tools do the sorts of things you’re looking for. Some will talk to the native UNIX user store. I do agree with the others, though: if you’re this far along, then it’s time to spin up LDAP and SSO, but this might be the same tool in your case.

Right now, I’m using Obsidian. I think I’d like to transition to keeping docs in a wiki, but I worry that it’s part of the self-hosted infrastructure. In other words, if the wiki’s down, I no longer have the docs that I need to repair the wiki.