Clear CIDs on potential session resumption

Updates the flight0handler to clear connection IDs in the event the
client is attempting to resume an existing session. If connection IDs
are to be used in the resumed session, they should be negotiated afresh.

https://datatracker.ietf.org/doc/html/rfc9146#section-3

Signed-off-by: Daniel Mangum <georgedanielmangum@gmail.com>

Author: hasheddan

flight0handler.go

@@ -22,6 +22,12 @@ func flight0Parse(_ context.Context, _ flightConn, state *State, cache *handshak
 		// No valid message received. Keep reading
 		return 0, nil, nil
 	}
+
+	// Connection Identifiers must be negotiated afresh on session resumption.
+	// https://datatracker.ietf.org/doc/html/rfc9146#name-the-connection_id-extension
+	state.localConnectionID = nil
+	state.remoteConnectionID = nil
+
 	state.handshakeRecvSequence = seq
 
 	var clientHello *handshake.MessageClientHello