In a small saucepan, whisk together the brown sugar, cornstarch, cayenne pepper, salt, and crushed pineapple with its juices until well combined. Whisk in the honey mustard.
Bring the saucepan to a low boil and simmer for 5 to 10 minutes until the sauce has thickened and is homogenous. Set aside and keep warm.
Chicken Thighs
Preheat a smoker to 350 degrees F (175 degrees C) or a drum smoker to 300 degrees F (150 degrees C).
In a large pan, heavily season the chicken thighs with the spice rub. Let rest for 15 minutes. Flip the chicken thighs over and heavily season the other side with the spice rub. Let rest for 15 minutes.
Place the thighs on the smoker, skin side-up, and cook for 15 minutes. Flip the chicken skin-side-down and cook for 20 additional minutes.
Increase the smoker temperature to 400 degrees F (205 degrees C). If using the drum smoker, drop the grill onto the middle rack.
Place the chicken thighs, skin-side-down, back on the smoker. Cook until the skin renders and becomes crisp and the internal temperature reaches 180 degrees F (80 degrees C), 5 to 10 minutes.
Let the chicken rest for 10 minutes, then serve with the Pineapple Sauce.