Rails 4 & devise & google oauth2

01_how_to_setup_google_auth_with_devise.md

• register a new project here
• set the followings under APIs & auth:
  • Consent screen: fill out the requires fields
  • APIs: Contacts API & Google+ API
  • Creditentials: create a new OAuth client ID
    • AUTHORIZED JAVASCRIPT ORIGINS: HOST (your app host) (protocol prefixed!)
    • AUTHORIZED REDIRECT URI: HOST/auth/google/callback (protocol prefixed!)
• sign in url is user_omniauth_authorize_path(:google)

devise.rb

Devise.setup do |config|
  # ==> OmniAuth Configuration
  config.omniauth :google_oauth2,
                  ENV['GOOGLE_CLIENT_ID'],
                  ENV['GOOGLE_CLIENT_SECRET'],
                  name: 'google',
                  scope: 'email, profile',
                  prompt: 'select_account',
                  image_aspect_ratio: 'square',
                  image_size: 50,
                  provider_ignores_state: true # hack, see: https://github.com/intridea/omniauth-oauth2/issues/58
  
  # ...
end

omniauth_callbacks_controller.rb

class OmniauthCallbacksController < Devise::OmniauthCallbacksController
  def google
    @user = User.apply_google_auth request.env['omniauth.auth'], current_user

    flash[:notice] = I18n.t 'devise.omniauth_callbacks.success', kind: 'Google'
    sign_in_and_redirect @user, event: :authentication
  end

  protected

  def new_session_path
    root_path
  end

  def after_omniauth_failure_path_for(_resource_name)
    root_path
  end
end

routes.rb

Rails.application.routes.draw do
  devise_for :users,
             path: '',
             controllers: { omniauth_callbacks: 'omniauth_callbacks' }

  devise_scope :user do
    delete 'logout' => 'devise/sessions#destroy', as: 'logout'
  end

  # ...
end

user.rb

# == Schema Information
#
# Table name: users
#
#  id         :integer          not null, primary key
#  email      :string(255)      not null
#  admin      :boolean          default(FALSE)
#  active     :boolean          default(FALSE)
#  name       :string(255)
#  image_url  :string(255)
#  created_at :datetime
#  updated_at :datetime
#

class User < ActiveRecord::Base
  devise :omniauthable, omniauth_providers: [:google]

  validates :email, :name, :image_url, presence: true
  validates :email, uniqueness: true

  def self.apply_google_auth(omniauth, _signed_in_resource = nil)
    user_info = omniauth.info

    User.where(email: user_info['email'])
        .first_or_create name: user_info['name'],
                         image_url: user_info['image']
  end

  def active_for_authentication?
    super && active?
  end
end