support servers that require authentication, including client certificate authentication

I need to download files from a service that requires authentication via client certificate and bearer token.

There doesn't seem to be a way to do this. Looking through the iOS docs, it does seem to be possible with the iOS platform API. I didn't look at the Android API yet.

Also, if anyone is interested in writing this, and making a PR, the company I'm working with would be interested in sponsoring this work for iOS and Android integrations.