Some services run really good behind a reverse proxy on 443, but some others can really become an hassle… And sometimes just opening other ports would be easier than to try configuring everything to work through 443.
An example that comes to my mind is SSH, yeah you can use SSLH to forward requests coming from 443 to 22, but it’s so much easier to just leave 22 open…
Now, for SSH, if you have certificate authentication or a strong password, I think you can feel quite safe, but what about other random ports? What risks I’m exposing my server to if I open some of them when needed for a service? Is the effort of trying to pass everything through 443/80 worth it?
while the most bare bones knocking implementation may be classed as obscurity, there’s certainly plenty of implementations which i wouldn’t class as obscurity.
Does this method use a cryptographically secure secret which is transmitted encrypted? If not, it is obscurity. If yes, just use normal secure authentication if your goal is security. If you want to get volume down and maybe reduce your risk, feel free to use such things but you should not apply the security label to it.