On macOS UserA can ask UserB to share their screen simply by entering UserB's Apple ID into a "New Connection" window in the macOS Screen Sharing app. Then, by some magic, Apple delivers the request to UserB as an alert on UserB's Macs, anywhere in the world:
| UserA would like to view your screen. [Accept] [Decline] [Block User]
Is there a Windows screen sharing app that UserA can use to make a connection in this way?
“Why do I ask?”, you ask.
- Why VNC? I already have to trust Apple because I run their OS, so for security it doesn’t make sense to hand over screen sharing on the server to a third party server-side app (including man-in-the-middle-attack opportunities for keyboard and mouse scraping). Apple provides VNC server software in macOS.
- Why not use an open port for VNC (via password-protected login). An open port is an invitation to get pounded with connection attempts 24x7. Any person/bot with a stolen username/password pair can get in at any time, 24x7.
- Why do I want the Apple ID trick? I want a human to have to be there at the server to approve each connection request. Also the trick works without an open port on my server. An Apple server does that for me by fielding connection requests.
Actually, letting any app on a non-Apple OS act as a VNC client is a bad idea for security reasons (See #1), so it seems the only good solution is to allow connections only from Apple's VNC app, running on macOS. And it seems clear that a client app that can do the Apple ID trick is not going to exist on any non-Apple OS (or on iCloud.com in a browser).
So my question is moot.