[jraph]

I could import the root certificate but instructions for activating it didn't work, they seem to apply on more recent versions of iOS.

[jeroenhd]

I've done it on iOS 9.3.5 and it worked in Safari at the very least. You need to import it first and then activate it from the settings afterwards, I believe.

iOS changed the exact procedure a few times so you may need to Google around for the exact steps you need to follow.