Stop forcing people to sign in with Google, facebook, twitter or github.
You’re so concerned with security that i’ve just been forced to disclose my mobile to google so i could sign up - thanks.
It’s properly dumb and irritating. You were slow enough to set up a forum and now deliberately stopping people contributing. You should be encouraging feedback not dictating what other tools people should have to use (and therefore what other details they have to disclose) to tell you. Typical old school bank attitude - and a really bad impression to give.