A friend of mine was connect to my private WiFi a while ago and did show me how Spotify connect plays on my Yamaha Receiver (RX-S600D).

There was no need to enter any authorization to access my reveiver.

Now he can even connect to my receiver and play music on it even when he's not connected to my WiFi network.

I don't see a chance how I can block this without removing my receiver from my home network, which is no option at all.

This is extremely annoying as he (accidentially)  starts to play music rather loud in the middle of the night on my receiver.

My receiver does not show any option to select spotify clients/accounts that may connect.

How can this be stopped??????