A Domain Secret or Authorization Code (AUTH-Code) is a code assigned by the Registrar at the time the domain name was registered. This Auth Code acts like a password for a domain name. Domain Secret is a security measure, ensuring that only the owner of the domain can transfer their domain name.
Code should be available within the Domain Name Management Interface provided by your Registrar. In the event that you are not able to locate your Domain (Transfer) Secret or Auth. Code, you need to contact the Support Team of your current Registrar, to obtain the same.