Minecraft, and consequently Sponge, has simple ban management to prevent unwanted users from joining your server.
/ban <name> [reason] command is a native Minecraft server function that bans player name. The complete list
of banned players is available using the command
It is also possible to ban any connections from a given IP address using
/banip <address|name> [reason]. The complete
list of banned IP addresses is available using the command
A ban can be reversed using the command
/pardon <name> or
More information on Bans can be found at the Minecraft Wiki.