A DESCRIPTION OF THE PROBLEM :
The launcher exe currently allows for 3 hardcoded variables: $APPDIR, $BINDIR and $ROOTDIR:
https://github.com/openjdk/jdk23u/blob/master/src/jdk.jpackage/share/native/applauncher/AppLauncher.cpp#L119-L121


However, it is not currently possible to to refer to the %APPDATA% folder or $HOME folder via variables in *.cfg files. Desktop applications will typically store userdata to %APPDATA%/Product or $HOME/.product so being able to access these values in *.cfg files would be very useful.

The exe launcher already reads these variables for other purposes but doesn't make the values available in *.cfg files:
https://github.com/openjdk/jdk23u/blob/master/src/jdk.jpackage/windows/native/applauncher/WinLauncher.cpp#L247-L248


Primary Feature Request:
* Make %APPDATA% and %LOCALAPPDATA% available in *.cfg files (for example via $APPDATA and $LOCALAPPDATA so that code that already exists can be reused)


Extended Feature Request:
* Extended the macro / replacement system to expand any environment variable, APPDATA, PATH, JAVA_OPTS, HOME, XDG_CONFIG_HOME, etc