Hanko is a golang server that implements passkeys and email based login.
It includes a Web component based GUI also and is very easy to integrate.
Or it can use go templates
for example the golang quickstart is here: hanko/quickstart at main · teamhanko/hanko · GitHub
I made an issue there also: caddy example · Issue #868 · teamhanko/hanko · GitHub
I would be willing to work on this with someone.
I would like to integrate it into the caddy website too. here: website/Caddyfile at master · caddyserver/website · GitHub
then it will make it very easy for people to add security to their caddy sites that used passkeys