Heat a pan and add sugar, lemon or lime juice, and water. Heat on med-high to dissolve all the sugar.
Once the mixture becomes translucent/clear then add garlic and red chili flakes. Turn temperature down to low.
Add Sriracha sauce and salt and let cook for a couple minutes. Make cornstarch slurry with the Tablespoon of cornstarch and Tablespoon of water and slowly add to sauce while stirring rapidly.
Notes: You can substitute rice vinegar for the lemon or lime juice. The sauce does thicken up after cooling so don't add too much cornstarch slurry and don't keep boiling for too long. If it becomes too thick or you need to re-warm, just add a small amount of water and return to stovetop.