app/controllers/users/omniauth_callbacks_controller.rb
class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
def facebook
@user = User.find_for_facebook_oauth(request.env['omniauth.auth'])
if @user.persisted?
sign_in_and_redirect @user, event: :authentication #this will throw if @user is not activated
set_flash_message(:notice, :success, kind: 'Facebook') if is_navigational_format?
else
session['devise.facebook_data'] = request.env['omniauth.auth']
redirect_to new_user_registration_url
end
end
end