Also known as Auth-Info code or EPP code, this is a password assigned by the domain name registrar as a security measure, needed to request a transfer of domains with extension: .Com, .Net, .Org, .Biz, .Mobi or .Info; and many others.
It emerged in March 2004 to try to stop the theft of domains (domain hijacking) and enhance the security for domains owners, but it was not until late October 2006, that Verisign implemented in the .Com and .Net domains, but this code it was previously being used in other extensions such as .org, .info .biz, .name, .pro and .tv; even since 2001 this code was used by some registrars.
The .Es (spanish cctld) and .Eu (europe) do not use this authorization code (the transfer is validated with an e-mail). Although the generic domains are not the only ones who need auth-code, there are many ccTLD domains (country code) also use them.
If you don`t see this code at your control panel, you can ask your domain registrar/provider, who will tell you what to do to get it. This password is mandatory and necessary to request the transfer of the domain.
Do not confuse the Auth-Code with internal codes of some registrars, the auth-code is only to transfer domains between registrars and not for internal transfers between users of the same registrar company. Some registrars have special codes to make transfers between users, inside of the registrar database (this code is not valid as an auth-code). Other registrars have internal codes to make changes to the domains (administrative data or DNS records) or to provide access to computer technician of the company (to change the DNS configuration, etc.).
To transfer a domain, we must take into consideration that there are to get the auth-code (the time we will spend depends on if you can get out of your control panel or you need to ask to your registrar, this task can bring you 2 minutes to several days), we must consider that the transfer takes 7 to 15 days (average). So when you want to transfer a domain name, you need to take the auth-code, almost 1 month in advance.
Many low-cost companies tend to retain your domains, block them 30 days before the renewal date. So the owner must pay the renewal in advance and then he can transfer the domain, for what is also crucial to work with a reliable registrar, even if you have to pay a little more.