How do you return validation errors ? about doorkeeper-grants_assertion HOT 3 CLOSED

I guess the easiest would be to raise an instance of DoorkeeperError (aka StandardError), eg:
raise Doorkeeper::Errors::DoorkeeperError.new('email already exists')

from doorkeeper-grants_assertion.

Or another idea, however I do not know if it will serve your case. Why not to check the existing users against fb_id OR email? Something like

user=User.where('fb_id=? or email=?',user_data["id"],user_data["email"]).first

In such a way, you can match and log in the user by email, possibly updating the fb_id if it is empty.

from doorkeeper-grants_assertion.

Thanks a lot @matfiz, second solution was bang on!

from doorkeeper-grants_assertion.