add oauth with google

config/initializers/devise.rb

@@ -271,7 +271,12 @@ Devise.setup do |config|
   # ==> OmniAuth
   # Add a new OmniAuth provider. Check the wiki for more information on setting
   # up on your models and hooks.
-  # config.omniauth :github, 'APP_ID', 'APP_SECRET', scope: 'user,public_repo'
+  config.omniauth(
+    :google_oauth2,
+    ENV['GOOGLE_OAUTH_CLIENT_ID'],
+    ENV['GOOGLE_OAUTH_CLIENT_SECRET'],
+    {}
+  )
 
   # ==> Warden configuration
   # If you want to use other strategies, that are not supported by Devise, or