Using selfsigned SSL Keys for a PWA on Android

Generate selfsigned ssl keys with:

HOSTNAME=melodypond
openssl genrsa -out ssl/snakeoil.key
openssl x509 -new -key ss/snakeoil.key -out ssl/snakeoil.crt -subj "/CN=$HOSTNAME" -extfile ssl/options.txt
# Then manually copy the key and certificate to /etc/ssl on the server.
#   and onto the Android device used as the controller.

These keys can then be added to the Android device used as the controller by going to Settings >> Security >> Credentials >> Install >> CA then selecting the certificate and rebooting the device.

If you are using a Firefox-based browser on the phone, you will also need to enable third party certificates in the Firefox app's developer settings. This can be accessed by tapping the logo on the about screen many times, then going to Settings >> Secret Settings >> Use Third Party CAs

Firefox should now show the site as secure and allow installing the PWA.