New Zealand domains have a UDAI (Unique Domain Authentication Identifier) - a randomly generated 8 character string unique to each NZ domain. The main purpose of a UDAI is to authorise the transfer of a domain from one registrar to another. A UDAI is initially generated when a domain is registered, although a new UDAI can be requested at any time.
International domains often use an Auth Code or EPP Code, which is very similar to a UDAI.
Having a valid UDAI or Auth Code gives a person virtually complete control over the domain name. Keep this in mind before passing the UDAI onto anyone else as they can potentially take over complete ownership of your domain.
Registrars are required to provide your UDAI upon request. SiteHost does not store the UDAI for your domain, but provides a method for you to request a new UDAI which will be generated and sent to the domain registrant email address.