I want to plumb the ZooKeeperServer object into the auth plugins so that I can store authentication data in zookeeper itself. With access to the ZooKeeperServer object, I also have access to the ZKDatabase and can look up entries in the local copy of the zookeeper data.
In order to implement this, I make sure that a ZooKeeperServer instance is passed in to the ProviderRegistry.initialize() method. Then initialize() will try to find a constructor for the AuthenticationProvider that takes a ZooKeeperServer instance. If the constructor is found, it will be used. Otherwise, initialize() will look for a constructor that takes no arguments and use that instead.