This is called URL Protocol Handler and you were following the right path of modifying the registry. HKEY_CLASSES_ROOT in fact maps to either HKEY_LOCAL_MACHINE\Software\Classes (which can have issues with write access) and HKEY_CURRENT_USER\Software\Classes, we use the latter.
Note : Ensure that Qt is compiled, and build the application using the release mode of Qt Creator, not the debug mode.
Here's the complete example that works:
