@alexivanov Basic Auth == HTTP authentication. That's entirely unrelated.
But look at how clients like MustardMod use OAuth to authenticate. That's perfectly usable without registering the client as an "app" (more than by logging in, which you have to do anyway of course).

There are tons of clients out there that use OAuth without the need to register the app with the server. Lots of examples. I don't develop any of those myself, so I can't give any quick tips on how to implement it. But there are multiple OAuth libraries available for all programming languages.