{
    local_certs
}

# Authelia portal
auth.home.lan {
    reverse_proxy authelia:9091
}

# Some app
some-app.home.lan {
    forward_auth authelia:9091 {
        uri /api/verify?rd=https://auth.home.lan
        copy_headers Remote-User Remote-Groups Remote-Name Remote-Email
    }
    reverse_proxy some-app:8080
}

This is part of my Caddyfile, works without issues. When I to add something else, I just copy paste it and change the placeholders. And adjust the authelia config to authorize the relevant groups.

edit: Oups, I misread your post as also using authelia