Can't sign in to YouTube via iMovie on iPhone 6

I'm trying to upload a video from iMovie to YouTube. When I try to sign in to YouTube through the iMovie app's share feature, I sign in successfully. But then it takes me to a page showing my Google account security settings. On the top left, there's a button that says "done." If I click on "done," it takes me back to the log-in screen and I have to input my YouTube username and password all over again.

In short, I'm signing in successfully but keep being redirected to the Google security settings page. When I click "done" to get out of it, I need to sign in again.

Does anyone know how to fix this?

For the record, I already know I can export to Camera Roll and upload from there. It would be nice to do it directly from iMovie, though.

Thanks for any pointers.