Epix

Well, that player didn't tell me, but he did do damage to our private server. I think maybe he use a common/weak password or maybe a friend of him just guessed the password and wanna troll him.

Well it's something like two-factor authentication. It's a shame but someone's password was leaked before. And I can't change mojang account login mechanism. When I using authme(or another bukkit plugin that allowed third party auth, can't remember the name) before, there were bugs to allow player do bad things when he have logged in the server but not provided password. Since all plugins have to let player type server command to auth, they have to allow player logged in before auth. So I want to make a mod to auth BEFORE a player entity can join the server. Will there still be a change to break things? If so, is it possible to use other methods to prevent that?

Probably because password distribution is easier than accessing the file and adding the information. I think you need to be more specific on the data you want to check. In my situation, it's extra authorization data input by user. I do know online-mode, whitelist, authme plugins, but I still need another password-like thing for a special server. It is asked when minecraft started by popping up a input box, and I want to verify it before player joined server. It would have to be a server and client mod. You will need a custom gui and custom packet. yeah I've written a gui to allow user type in information. But how to use custom packet? I have used SimpleNetworkWrapper before, but is it possible to use it before player joining world and prevent login if verify fails? Any hint of which class or event I should use is okay...

I think you need to be more specific on the data you want to check. In my situation, it's extra authorization data input by user. I do know online-mode, whitelist, authme plugins, but I still need another password-like thing for a special server. It is asked when minecraft started by popping up a input box, and I want to verify it before player joined server.

I wanna write a mod to verify extra data on connecting server (before player joining world to prevent potential damage). I've written mods before but my knowledge about network is only limited to SimpleNetworkWrapper. Maybe I should use ClientConnectedToServerEvent? But I can't find many useful examples or documents about it. Any help is appreciated!

PlayerLoggedInEvent won't be triggered on a client side mod when joining a server. Don' know if it's designed to do so? BTW I'm using EntityJoinWorldEvent and it seems working well on client side.