Currently, the ProxyConfig interface does not expose anything related to player info forwarding. This is quite unfortunate if you need to access the forwarding mode (and secret) from your plugin. (For example, to send the secret to a built-in limbo).

The workaround to this issue is quite simple, import the velocity API implementation, cast the configuration to VelocityConfiguration, and then you can get the forwarding config. But, I believe that it is quite unfortunate to need to use the velocity API implementation directly.