Implement Google OAuth2 authentication

app/controllers/users/omniauth_callbacks_controller.rb

@@ -2,13 +2,22 @@
 
 class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
   def github
+    handle_auth('GitHub')
+  end
+
+  def google_oauth2
+    handle_auth('Google')
+  end
+
+  private
+
+  def handle_auth(provider)
     @user = User.from_omniauth(request.env['omniauth.auth'])
 
     if @user.persisted?
-      flash[:notice] = I18n.t 'devise.omniauth_callbacks.success', kind: 'GitHub'
+      flash[:notice] = I18n.t 'devise.omniauth_callbacks.success', kind: provider
       sign_in_and_redirect @user, event: :authentication
     else
-      session['devise.github_data'] = request.env['omniauth.auth'].except('extra')
       redirect_to new_user_registration_url, alert: @user.errors.full_messages.join("\n")
     end
   end

app/models/user.rb

@@ -4,7 +4,7 @@ class User < ApplicationRecord # rubocop:disable Metrics/ClassLength
   include UserFamily
   devise :database_authenticatable, :registerable,
          :recoverable, :rememberable, :validatable, :trackable,
-         :omniauthable, omniauth_providers: %i[github]
+         :omniauthable, omniauth_providers: %i[github google_oauth2]
 
   has_many :points, dependent: :destroy
   has_many :imports,        dependent: :destroy

config/initializers/devise.rb

@@ -266,6 +266,8 @@ Devise.setup do |config|
   # Add a new OmniAuth provider. Check the wiki for more information on setting
   # up on your models and hooks.
   config.omniauth :github, ENV['GITHUB_OAUTH_CLIENT_ID'], ENV['GITHUB_OAUTH_CLIENT_SECRET'], scope: 'user:email'
+  config.omniauth :google_oauth2, ENV['GOOGLE_OAUTH_CLIENT_ID'], ENV['GOOGLE_OAUTH_CLIENT_SECRET'],
+                  scope: 'userinfo.email,userinfo.profile'
 
   # ==> Warden configuration
   # If you want to use other strategies, that are not supported by Devise, or