After some time (usually 15-30 minutes) authentication server starts working again, so most people can join the server.
Most, because some people seems to be blocked from joining crpg servers, but can join other servers (native) without problems.
So there are actually two issues same time.
First is bugged authentication server, after too many connections from WSE2 clients same time. With this issue, you get "Unable to connect to server" message.
Second is "Incorrect authorization key" message, which happens only to some people. If you are unlucky, when authentication server start working again, you will get "Incorrect authorization key" message, and then you won't be able to join cRPG servers for next few hours. You can join native servers without problems though, so it's only related to crpg servers for some reason.