fix https://github.com/rustdesk/rustdesk-server/issues/435

src/rendezvous_server.rs

@@ -680,6 +680,7 @@ impl RendezvousServer {
     ) -> ResultType<(RendezvousMessage, Option<SocketAddr>)> {
         let mut ph = ph;
         if !key.is_empty() && ph.licence_key != key {
+            log::warn!("Authentication failed from {} for peer {} - invalid key", addr, ph.id);
             let mut msg_out = RendezvousMessage::new();
             msg_out.set_punch_hole_response(PunchHoleResponse {
                 failure: punch_hole_response::Failure::LICENSE_MISMATCH.into(),