I have done this trip at least 6 times this year and you do NOT need to leave the secured area if you have carry-on bags. I have never been successful checking in on line but have tried a couple of times. You need to go down to the IC gate and they will check you in and print a boarding pass. Be careful, they do close the flight 30 minutes before flight time and 1 hour before the flight you won't find anyone at the gate.