Coach Dan John has a "fun" challenge where you back squat your bodyweight 50 times in a single set without racking the bar. I tend to favor the front squat to the back squat, especially when you're pushing yourself to the brink, because holding the bar in front helps keep form in check. Having the bar on your back allows you to grind out ugly rep after ugly rep, but with the front squat, you'll just end up dumping the bar if your form slips and you start to lean forward too much.
To adapt the challenge to the front squat, your goal is to complete 50 front squats in four minutes. You can break it up into as many sets as you want and you can choose your rest intervals. The clock starts when you unrack the bar for the first set and ends when you rack the bar after completing your 50th rep.
The 4-Minute Front Squat Challenge
Start with a weight you could squat for about 25-30 reps (i.e. very light) with the ultimate goal of completing all 50 reps with your bodyweight on the bar. Once you achieve that, to step it up even further and eliminate the need to fuss around with a lot of small plates, use the following weight guidelines:
Bodyweight 135 pounds and under: Use 135
Bodyweight 136-185 pounds: Use 185
Bodyweight 186-205 pounds: Use 205
Bodyweight over 205 pounds: Use 225
The key is to work on your pacing so you don't blow your load too early. I originally set this as a 5-minute challenge and gradually worked down to 4 minutes, so it may be wise for you to do that too.