I have a Google App Engine project. On this project I have setup a custom domain and an SSL certificate. Therefore, I can use https://www.mysite.xxx, http
https://www.mysite.xxx
http
So you can add "secure: always" to your yaml file
https://cloud.google.com/appengine/docs/python/config/appconfig?hl=en#Python_app_yaml_Secure_URLs