what exactly is "when I try https://MYSERPSERVERIP/api/3/SDVc or any other register, it requests for a username and password"?
How can you see that OAuth it asks for password? OAuth just replies with some code such as "server_error" or smth.

Try to play in google OAuth playground and you should see what happens.
I have no problems getting data via OAuth, except some registers can cause server crash (already reported as a bug)