OAuth2: signal callbackDataReceived not emitting in QOAuthHttpServerReplyHandler

According documentation QAbstractOAuthReplyHandler::callbackDataReceived signal must be emitted before parsing callback data, but as I can see it, only callbackReceived signal emitting.
It can sometimes be useful to get callback data. For example it can be used in implementation of the Implicit Grant Flow, where response data is placed in a URL fragment.