I swear one day these websites like haveibeenpwned.com and the like will start collecting the data you enter

• caddy can do that with basicauth: https://caddyserver.com/docs/caddyfile/directives/basicauth
• nginx can 100% do that because it has plugins for everything
• apache can probably do something like that

most reverse proxies have SSO tooling that you can set up pretty easily

But honestly, have you considered just using wireguard for these cases? It’s much more secure if you just want a bunch of stuff hidden from the rest of the world