Trust custom CA in electron-builder's autoUpdater, without importing to system

Question

How can we programmatically make the autoUpdate of electron-builder trust a specific custom CA certificate when fetching updates using the GenericHTTPServer provider? The solution should not involve importing the certificate to the system and should be portable to all platforms: linux, macOS and windows.

I'm neither a node.js nor an electron expert. There seem to be a number of different API's around for accessing resources via HTTP, and I don't know which of those are used by the auto-updater. The following things I have tried:

• electron.app.importCertifictate: Does not exist on macOS (and according to the docs, neither on windows). I haven't tried it on linux.
• Handling the electron certificate-error: Does not seem to be triggered when auto-updater checks for updates.
• Using the NODE_EXTRA_CA_CERTS environment variable did not have any effect. Also, this comment on a electron-builder GitHub issue suggests that electron-builder uses the electron http services, not those of node.
• The documentation of the electron.net API claims that it tries to follow closely the Node API, but does not mention anything related to certificates.