Download the binary, make a Caddyfile
myservice.example.com { basic_auth { admin some_password_hash_here } reverse_proxy :3000 }
domain1.com -> service on port 1234
domain2.com -> service on port 5678
domain3.com -> serving a file directory.
And then you still access domain1.com, domain2.com, domain3.com on port 80/443
Download the binary, make a Caddyfile
And then just "./caddy start"