Preheat the oven to 450 degrees F (230 degrees C). Line a rimmed baking sheet with foil and spray with cooking spray.
Combine garlic, sage, salt, and pepper in a small bowl and mix well. Rub mixture over all surfaces of the pork. Place pork on the prepared baking sheet.
Roast in the preheated oven until browned on top, 20 to 25 minutes.
While the pork is cooking, whisk together vinegar, water, soy sauce, brown sugar, mustard, and cornstarch in a small bowl.
When pork is browned on top, remove from the oven and reduce oven temperature to 325 degrees F (165 degrees C).
Lightly coat the top of the pork with 1/2 of the glaze mixture. Return to the oven and cook until the internal temperature reaches 145 to 150 degrees F (63 to 65 degrees C), about 45 minutes. Pour the remaining glaze over the pork during the last 5 to 10 minutes of cooking.
Remove from the oven and lightly tent with foil. Allow to rest for 10 to 15 minutes.
Slice pork and serve with pan drippings and juices.