Yep, merlin was right. Whenever your bike is nearly upright, you can brake hard. You can choose lines that allow you to go straighter for a longer period if you want to slow even further.

For the turns, let it go. Braking in a turn lowers your cornering traction anyway (actually can make you more likely to slide out). You can also take advantage of a larger turn radius (curve might loosen up a bit) to go nearly straight again momentarily, and grab some brake there.

Lastly, if you get in a bad spot and must brake in a hard turn, don't use any rear brake. Much more likely to slide out that way. Just smoothly grab some front and hope for the best. Keep everything smooth (not gradual necessarily, just smooth).

Get this stuff figured out before your first rain descent.