An auth code is like a key that you get when you purchase a domain by auction or buy a domain.You will need such an auth code to move domains to a new provider. If you win an auction at nicsell and we could catch the domain successfully you will get the auth info by mail.
With this you can go to your desired hosting service to deposit your domain on their server. Your provider might require further information from you.
It is also important that you move the domains in a timely manner, so that no additional costs come about. If Domains are remaining a long time on the server, hosting costst can be billed from you.
This auth code method for .de domains exists since 2010 and the moving of a domain without auth code is no longer valid.
An auth code for .de domain is valid up to 30 days but could be regenerated afterwards.