Encrypt connection to servers on higher versions

[Rigner]

Feature description

In 1.20.5, Minecraft added the ability the encrypt the connection even when in offline mode. It would be great to add support for this mechanism as well to improve security and privacy.

A new boolean was added to the Encryption Request packet to tell if the client should authenticate to Mojang or not.
https://minecraft.wiki/w/Java_Edition_protocol#Encryption_Request

Right now, this is never used in a normal minecraft server, but could be added at some point. If the server sends the packet (I made my own test), the user gets disconnected because of this check:

BungeeCord/proxy/src/main/java/net/md_5/bungee/ServerConnector.java

Line 412 in 4dad940

throw new QuietException( "Server is online mode!" );

Goal of the feature

Make the bungee <-> server connection more secured.

Unfitting alternatives

None.

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[Outfluencer]

This was already discuessed in mutiple pull request. I personly would like to implement this for backend and frontend.

Here a PR that wanted to add Client -> Proxy encryption #3749

I see multiple benefits.

For backend the traffic can not be intercept anymore that easy, only with an MITM attack.
For frontend the player heads in the tablist would be displayed (could be a much wanted feature by offline mode servers), and the traffic is also not interceptable anymore that easy, but there still is a generell MITM risk as with the backend connection.

Both would generally improve security at performace cost.

[Rigner]

My bad, didn't see the PR 😅