If me I'd leave it in the short term covered park by the domestic terminal.
Motorbikes can park anywhere in the Airport parking areas if they use a car parking space.
I have seen motorbikes parked in the uncovered areas too and you should be OK, Auckland airport is pretty much a 24hr operation and there is a lot of security about all the time. Park close to, and in view of the road or terminal and you should be fine. Map and other info
here.
There are a few off site parking places that run a shuttle service to the airport, don't know if they take bikes but are cheaper. For one night it's probably not a biggie. Try
www.aeroparks.co.nz,
www.flypark.co.nz,
www.skyway.co.nz
I have often left my car in the long term covered park and been very happy with the security.
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