DIAGNOSIS That's condensation, and it means the room's air is too humid and warm for the cooler's current temperature setting. The glass is colder than the room's dew point.
FIX You need to adjust the balance. First, turn the internal thermostat dial to a slightly warmer setting (a lower number). The goal is to have your drinks cool, not ice-cold. Second, improve room air circulation. Make sure the cooler isn't crammed in a tight cabinet or corner. A small fan pointing near it can work wonders. Third, wipe the door dry completely to reset it.
IF THAT DIDN'T WORK If the sweating is between the glass panes (inside the door itself), that indicates a broken seal and moisture has gotten into the insulated gap. The door would need to be replaced, as it's not serviceable.
HEADS UP Never use a towel or cloth to block the bottom vent grille in an attempt to stop the cold air "leak." That vent is crucial for the compressor to exhaust heat. Blocking it will cause the unit to overheat and fail.