Setting up OmniAuth for Google Login

Setting up OmniAuth for Google Login

[From this tutorial](https://medium.com/@ajayramesh/social-login-with-omniauth-and-rails-5-0-ad2bbd2a998e)


# 1. Register your app with Google, get credentials and secret
# Authorized redirect should be: http://localhost:3000/auth/google_oauth2/callback
# enable Google+ API and Contacts API

# 2. Include OmniAuth gem in gemfile:
# gem ‘omniauth-google-oauth2’

# 3. Configure OmniAuth:
# config/initializers/omniauth.rb

Rails.application.config.middleware.use OmniAuth::Builder do
  provider :google_oauth2, "[Client ID]", "[Client Secret]"
end

# 4. Create the User model
# $ rails g model User provider uid email first_name last_name picture

# 5. migrate the db: $ rails db:migrate

# 6. Use hash returned from Google to look up user in the db: 
# models/user.rb:

class User < ApplicationRecord
	def self.find_or_create_from_auth_hash(auth)
		where(provider: auth.provider, uid: auth.uid).first_or_initialize.tap do |user|
			user.provider = auth.provider
			user.uid = auth.uid
			user.first_name = auth.info.first_name
			user.last_name = auth.info.last_name
			user.email = auth.info.email
			user.picture = auth.info.image
			user.save!
		end
	end
end

# 7. Configure the routes.  routes.rb
Rails.application.routes.draw do
  get 'login', to: redirect('/auth/google_oauth2'), as: 'login'
  get 'logout', to: 'sessions#destroy', as: 'logout'
  get 'auth/:provider/callback', to: 'sessions#create'
  get 'auth/failure', to: redirect('/')
  get 'home', to: 'home#show'
  get 'me', to: 'me#show', as: 'me'

  root to: "home#show"
end

# 8. Create Home and Me controllers (Session controller will be created later w/o the view)
# home_controller.rb
class HomeController < ApplicationController
  def show
  end
end

# me_controller.rb
class MeController < ApplicationController
  before_action :authenticate
    def show
    end
end

# 9. Create sessions controller only: $ touch app/views/controllers/sessions_controller.rb
# add the following:
class SessionsController < ApplicationController

  def create
    @user = User.find_or_create_from_auth_hash(auth_hash)
    session[:user_id] = @user.id
    redirect_to :me
  end

  def destroy
    session[:user_id] = nil
    redirect_to root_path
  end

  protected
    def auth_hash
      request.env['omniauth.auth']
    end

end

# 10. Add the following methods to application_controller.rb
class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception
  helper_method :current_user

  def authenticate
    redirect_to :login unless user_signed_in?
  end

  def current_user
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end

  def user_signed_in?
    # converts current_user to a boolean by negating the negation
    !!current_user
  end

end

# 11. Create Views:
# home/show.html.erb:
<h1> Welcome, please login to continue </h1>
<a href="/login">Sign in with Google</a>

# me/show.html.erb
<% if current_user %>
  <% current_user.attributes.each do |k, v| %>
    <b><%= k %>:</b> <%= v %> <br>
  <% end %>
<% end %>