How do I sign an MSI using javafxpackager?

I'm actually using javafxpackager through the JavaFX-Gradle-Plugin, but I can't figure out the solution in plain javafxpackager, so, that would help as well.

How do I sign an MSI using javafxpackager? How do I specify the cert/key/whatever is needed?

In its documentation:

• https://docs.oracle.com/javase/8/docs/technotes/tools/unix/javafxpackager.html
• https://docs.oracle.com/javase/9/tools/javapackager.htm

I can see the options for Mac OS, such as: mac.signing-key-developer-id-app=key but I don't see anything about signing the Windows MSI installer.

In this doc:

• https://docs.oracle.com/javafx/2/deployment/self-contained-packaging.htm

it acknowledges the need for signing it by saying:

If you plan to distribute your MSI package on the network, then consider signing it for the best user experience.

but there's no explanation on how to achieve this (compared to the Mac OS equivalent section).

It turns out javafxpackager doesn't do this and you can simply sign an MSI after it's been generated:

https://pevma.blogspot.de/2014/02/signing-windows-installation-msi.html

https://howdididothatthingagain.blogspot.de/2013/02/burn-02-how-to-sign-msi-packages-and.html