Create a plugin to auto ban any player expect the players whose names are in a whitelist file and the operators. It must create the whitelist file by it's own. As, soon as any new player enters the server, this plugin will collect the name of the player from the chat message where it says "(A player) has joined the game, and to ban the player it will use console and execute the command "/ban (The name)". And for the whitelist file, create a command which will add player names to the whitelist, the command may look like "/ab add (player name) wl" here the "ab" refers to "Axe ban" the plugin name and "wl" refers to "whitelist". similarly create one more command for removing player name from the whitelist, it will be "/ab remove (player name) wl" like this.