Comment by noirscape

It's technically possible to get any Android app to accept user CAs. Unfortunately it requires unpacking it with apktool, adding a networkconfigoverride to the XML assets and pointing the AndroidManifest.xml to use it. Then restitch the APK with apktool, use jarsigner/apksigner and finally use zipalign.

Doesn't need a custom ROM, but it's so goddamn annoying that you might as well not bother. I know how to do these things; most users won't and given the direction the big G is heading in with device freedom, it's not looking all that bright for this approach either.