Hi there, one of the simplest method would be to use a current state node to check the status of HA master switch. In accordance to the switch state, you can either continue the flow or reject it.
If you have any more doubts in implementation, please do ask
If you want to disable an entire flow tab you can use this. In the http nodes enable authentification and use basic with your HA name and password. I’m not using https so it may be different if you do.