Add OAuth2 authentication (#147)

- Added Site settings > Authentication section
- Create/edit/delete your custom oauth2 configurations
- Login or signup with oauth2

app/controllers/application_controller.rb

@@ -47,6 +47,12 @@ class ApplicationController < ActionController::Base
       I18n.locale = @tenant.locale
     end
 
+    def load_oauths
+      @o_auths = Current.tenant_or_raise!.o_auths
+        .where(is_enabled: true)
+        .order(created_at: :asc)
+    end
+
   private
 
     def user_not_authorized