BungeeGuard setting breaks Forge 1.12 compatibility

[austin4195]

Steps to reproduce:

1. Setup proxy and one modded forge backend server
2. Set proxy to announce-forge to true, ping-passthrough "mods", and forwarding mode to "bungeeguard"
3. Attempt to connect with BungeeGuard installed on backend server

Expected result Successfully joining the server

Result encountered Disconnect from backend server saying "this server requires mods"

Additional notes WaterFall + BungeeGuard does not reproduce this error. Additional testing using VelocityGuard and setting forwarding mode to "legacy" works. My thought is that the proxy is not relaying the client mods to the server when set to "bungeeguard" mode as the client presents as a vanilla client even though mods are installed. When set to "legacy" the mod list gets passed to the backend server. The proxy is able to passthrough the mods to the client but not able to send the client mods to the backend server.

Velocity Version: 3.1.1

[Xernium]

I am not sure what mod is adding Bungeeguard to your backend server this is very much intentional. Velocity also doesn’t announce forge in legacy forwarding mode- the data would conflict. Spongeforge solves this by ignoring the forge data if legacy forwarding is configured.

[austin4195]

No mods are adding BungeeGuard to the backend server. It is installed on its own from here. The "legacy" mode has been working with VelocityGuard which tells me that something might be borked in the handshake packet when set to "BungeeGuard" mode.

This is also referenced in issue #701 only this is confirming the issue with a more standard setup and not a fork of BungeeGuard as seen in this issue