> Does every minecraft client have to authenticate with a central server before joining a private one? Yes. The way it works is that when a client attempts to

> Does every minecraft client have to authenticate with a central server before joining a private one? Yes. The way it works is that when a client attempts to join a (private) server, it sends the user id to the private server, and then sends Mojang a message informing them they it's trying to connect to a server at this address. The private server then asks Mojang if the supplied user id is valid, and attempting to sign in to the server at this address. Mojang then replies to the server confirming the authentication of the client, and then the server lets them in. There's also an exchange of cryptographic keys mixed in there, but that's the basics.