[winswitch] xpra macOS support

[Antoine Martin]

(..)
> I did a clean install of Big Sur on a different system and was able to
> access that
> from a Windows 10 system - both systems are on the ethernet network where I
> work. To get a working connection to the Big Sur system, I started the
> xpra GUI
> on the Big Sur system and manually started the xpra shadow server using the
> "Shadow" button in the GUI, i.e. I haven't been able to establish a
> connection to the
> Big Sur system by initiating the connection from the Windows 10 system when
> the Shadow server isn't already running on the Big Sur system.
Right. There is currently no way to initiate a new shadow session on a
windows or macos system through the GUI.
This used to be possible using the command line:
xpra shadow ssh://HOST/
That was using a macos agent, so you wouldn't need to be logged in.
But they've changed something, so this no longer works.
(I'm not sure how / if this can be fixed with newer versions of macos)

> If you weren't aware of this, the first time the Shadow server is
> started on a
> Big Sur system, macOS prompts you with
> 
> 
>      "sh" would like to record this computer's screen.
> 
>      Grant access to this application in Security & Privacy
>      preferences, located in System Preferences.
> 
> 
> If you click the "Open System Preferences" button, an "sh" item is added to
> "Security & Privacy | Privacy | Screen Recording", but if you don't
> place a check
> mark in the box to the left of "sh" in "Screen Recording", the effect of
> clicking
> the mouse buttons or pressing keys on keyboard, on the system you're
> connnecting from, isn't displayed on the system you're connnecting from.
Ah, that explains what I've been seeing when I last checked.
(maybe I missed the prompt?)

The name will eventually be changed from "sh" to a more useful and
recognizable name if I ever try again to get the app notarized.
(as Apple is unable to sign shell scripts)
But this costs a yearly fee and is quite tedious, so this may take a while.

> For example, if I position the mouse cursor of my Windows 10 system on the
> Apple menu in the xpra window for the Big Sur system and left click, the
> Apple menu opens on the Big Sur system but that activity isn't displayed
> in the xpra window on the Windows 10 system. The keyboard doesn't seem
> to work at all until the box to the left of "sh" is checked in "Screen
> Recording".

Thanks, for the details, this will help others.

Cheers,
Antoine