We recently released an update that allows Minecraft players to use our queueing system to join games and automatically track match scores. This means that a dynamic IP will be generated after the queue window pops, which you will use to join the match lobby.
In order to participate in the Spring matches, you will need to link your Mojang account so that your account gets whitelisted. To do this, go to your Game Connections, either by selecting the Connect Games link on the left of your dashboard or via your Account Settings>Game Connections. Then, find your Minecraft Game Connection and select the three dots on the far right to Edit. Then follow the instructions to link your Mojang account and you're all set!