The TTLSApplicationLayerProtocolNegotiationExtension class represents the application-layer protocol negotiation extension.
For instances in which multiple application protocols are supported on the same TCP port, this extension allows the application layer to negotiate which protocol will be used within the TLS connection. The client sends the list of supported application protocols as part of the TLS ClientHello message. The server chooses a protocol and sends the selected protocol as part of the TLS ServerHello message.
This extension is described in RFC 7301.