In a medium saucepan, combine pineapple juice, rice vinegar, brown sugar, ketchup, and soy sauce.
Whisk the mixture over medium heat until the sugar dissolves.
In a small bowl, mix cornstarch and water to create a slurry.
Slowly add the cornstarch mixture to the saucepan, stirring continuously.
Bring the sauce to a gentle boil while constantly stirring.
Once it thickens (about 2-3 minutes), reduce the heat to low.
Add garlic powder and grated ginger, stirring well.
Season with salt to taste.
Remove from heat and let it cool slightly.
Transfer the sauce to a glass jar and refrigerate if not using immediately.