In a gallon-size freezer bag, mix salt with warm water. Add the remaining Brine ingredients, including the pork. Brine for exactly 20 minutes then remove pork from brine, rinse and pat dry.
The pork becomes mealy if left in the brine any longer.
Meanwhile, whisk together the Cajun Rub spices in a small bowl. Remove 1 teaspoon for the Glaze. Whisk together remaining rub spices with 2 tablespoons olive oil. Rub the pork all over with this Wet Rub. Set aside.
Whisk together all of the Tangy Pineapple Glaze ingredients EXCEPT for crushed pineapple. Remove 1/4 cup Glaze for basting and set aside (“Basting Glaze”). Add the remaining Glaze to a small saucepan along with crushed pineapple (“Pineapple Glaze”). Set aside.
Preheat oven to 425 F degrees.
Heat 1 tablespoon vegetable oil in a cast iron skillet over medium high heat. When oil is very hot, add pork tenderloin. Sear each side until browned, approximately 1-2 minutes per side. Place tenderloin on rack in shallow roasting pan or on a lightly greased rack placed on a baking sheet and baste with half of the Basting Glaze.
Roast at 425F degrees F, for approximately 25 to 30 minutes, basting once with remaining Basting Glaze after 15 minutes. When done, an internal thermometer inserted into the thickest part of the tenderloin should register between 145 and 150 degrees F (63 and 65 degrees C). This means the pork will be juicy and slightly pink in the middle. Let cooked pork stand 10 minutes before slicing.
Meanwhile, heat Pineapple Glaze in the small saucepan just until warmed.
To serve, slice tenderloin into thin slices and top with Tangy Pineapple Glaze.