My app implements the Google and Facebook login. The trouble is that there seems to be no differentiation between “logging in” with Google and “registering” with google - they both go through the oauth process and create an account if one does not already exist.
I have users who register with my service using the normal email and password mechanism (say with a hotmail account), then discover the “Login with Google” button and think they can press that button and get logged in under their hotmail account! Result - two logins and confusion reigns.
I really only want to create a new account when the user clicks the “register with google” button and refuse login with “login with google” when the email does not exists.