Allow Joplin Apps to use Client Certificates

I've successfully configured NGINX as a reverse proxy for Joplin's Server via Docker. I would like to be able to configure my Android mobile app, and the desktop app, to push a client certificate to be sent to the web server.

My thinking is that this provides an extra layer of security, preventing from having Joplin exposed to anyone on the internet. I'd like to be able to sync notes publicly, without necessarily having to have my client VPN active.

While I was able to get this done via NGINX successfully, attempting to sync the Android app failed. The client certificate is installed properly, and works when visiting the Joplin server site via the browser, but the application doesn't seem to try any of the installed user certificates.

This is similar to this topic, but that topic points specifically to WebDAV.