Authorization code is used to get additional protection from unauthorized registrar change. In the process of registrar change registrant should provide the authorization code to aregistrar that will manage the domain name after the transfer. Without the authorization code or with a wrong authorization code the registry will decline the request of the new registrar for domain name transfer.
How to get the authorization code
If domain name registrant does not know the authorization code, he should contact the current registrar. As per ICANN's rules (for gTLD or ccTLD domain names and Foundation for Assistance for Internet Technologies and Infrastructure Development (for geodomains, EXNET.SU and RU.NET domains)), the registrar should provide the authorization code to the domain name registrant. Information, which is essential for the registrar in order to confirm that you are the domain name registrant, is determined by the registrar.
If RU-CENTER is your current registrar
You should send to email@example.com a request, where indicating the domain name and asking for an authorisation code for domain transfer to another registrar. In response to your request RU-CENTER will send you an authorization link. By authorizing you will confirm your domain management rights. Upon receipt of such confirmation RU-CENTER will send you the registry authorization code.