Disclosed is an authentication management system including a custom credential provider installed on a computing device to support OS account authentication through an alternate authentication method that replaces an OS account authentication method supported by an operating system of the computing device, and an authentication management server communicably connected to the custom credential provider via a communication network to perform user authentication related to a user who attempts to OS account authentication using the alternate authentication information when the OS account authentication based on the alternate authentication information used in the alternate authentication method is attempted and transfer, to the custom credential provider, account authentication information necessary to perform OS account authentication according to the OS account authentication method supporting by the operating system or a seed value that is based on generation of the account authentication information when the user authentication is successful.