A Sealed Connection
All traffic between the game and the server is now encrypted.
Everything that travels between your game and the server is now encrypted, including your password when you log in. Before this, the password crossed the network in the clear.
The client already knows which certificate the official server must present, so it cannot be fooled by another one. The server refuses any connection without encryption, and will not even start without its key — there is no fallback to an unprotected connection.