You’d need to get permission / get the gate unlocked at White Rock Station. You may also need to get permission to cross the Maori Land at the Cape Palliser end (albeit that I’ve heard that that part of the ride may have been easier to gain access to recently).
The track no longer follows the paper roads, so access is not a given.
There has also been a slip you need to ride over at the White Rock end that has provided access issues for some years. Not sure what that’s like currently.