The auth code is a six-to-16-character code assigned by the current sponsoring registrar that serves as a password for the domain. Auth codes are asecurity measure that ensures that only the owner of the domain name can make transfers.
If you do not know your auth code, you can obtain it from your registrar. Registrars are contractually required to provide the auth code upon the request by the registrant.
Registrars can obtain the auth code for their domain names by sending a request to the registry. Registrars are able to obtain auth codes only for the domain names that they manage.