As the user can register using Facebook, you can register the user using the Google Plus account?
I'm using Google translator, because I'm Brazilian and do not speak English.
you can use open login plugin:
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.