Brake before the turn, not in the turn, if at all possible (hey, we all get it wrong sometimes). You should not be braking in the turn, that is for emergencies only and is an indication that you've misjudged the turn and should have braked more before entering it (or that you should have chosen a different line through the turn).
Modulating your speed with the rear brake is fine, it can save wear on the front brake for when you need it. There are a few other times you want to use the rear brake - slippery surfaces (wet, gravel) to avoid washing out front wheel; while turning (if you've misjudged your speed or the sharpness of a turn), again to avoid washing out front and to avoid high-siding. However, to slow significantly or stop from a high speed you need to use the front brake.
Last edited by noimagination; 07-16-21 at 06:14 AM.