broadwayd
When using broadwayd, specify the display number to use, prefixed with a colon, similar to X. The default display number is 0.
broadwayd :5
Then point your web browser at http://127.0.0.1:8085. Start your applications like this:
GDK_BACKEND=broadway BROADWAY_DISPLAY=:5 gtk3-demo
You can add password protection for your session by creating a file in $XDG_CONFIG_HOME/broadway.passwd or $HOME/.config/broadway.passwd with a crypt(3) style password hash. A simple way to generate it is with openssl:
openssl passwd -1 > ~/.config/broadway.passwd
--port
--address
--unixsocket