Environment Variables cannot be accessed

[Vonor]

Apparently in VS Code you can use ${env:SOMEVAR} to use the environment variable's content.
However, in a powerHeader template setup I am trying the following:

settings.json

    "powerHeader.variables": [
      "<author>=\"${env:USERFN}\"",
    ],
    "powerHeader.template": "Author: <author>"

Upon inserting the header into a new file I get

Author: USERFN

This seems to be a bug in my opinion. Or is there another way of doing that, which I couldn't find in the documentation?