Have you looked at the Forgot Password module in the appstore? Are your already using it ?
If you’re already using it and you want to skip a re-authentication you would have to do that in Java. Personally I would suggest against it as you’d have a new login flow (via your new MF) which could become a security risk down the line if not maintained.
Edit: If you still want to do it, in a java action use this command:
Core.authenticate(getContext(), User, Password);
Hope this helps
I had downloaded the forgot password module in mendix 7 and got some errors