An auth code (short for authorization code) is a string of random letters and numbers used to prevent domain hijackers from transferring a domain without the owner's permission. Authorization codes must be retrieved from the current domain registrar. Auth codes are also sometimes referred to as EPP code or authinfo code or secret key.

Domains ending with .com, .net, .org, .info, .biz, .us, and .cn require authorization codes for domain transfers.