I was getting "Authentication Credentials Required" message with the version 45.0.2552.812. I tried wiping the entire data including passwords and relaunched the browser to find that the problem still persists.
I uninstalled Opera from my Mac and reinstalled it from the setup package that I have downloaded from opera.com. This time, Opera fails to connect to the VPN at all.
Any kind of help is appreciated.
It's fixed now. Probably, a temporary snag.