Duplicate of #3, please follow up there.
I have recently seen a certificate without CA flag that could be imported and used with DAVdroid in Android 4.4, so when I find time, there might be a CAdroid update that allows certificates without CA flag to be imported in certain Android versions. That would greatly improve user experience for DAVdroid users, too.
For more information, please see in #3, https://davdroid.bitfire.at/faq/entry/importing-a-certificate, and http://cadroid.bitfire.at/.
