The Authentication Server controls access to WWII Online's game servers. When this is offline you will be unable to login and access the game, as it acts as the "gateway" for all new incoming connections.
During these times Playnet staff is likely aware of it and working on a rapid solution. Keep checking every 20-30 minutes.
Be sure to check your account is also active at http://wwiionline.com/account. If your account is active but you're unable to access the game server it is very likely that the Auth Server is temporarily offline, which is rare but happens.