We have 3 separate environments(namely, version) for our app which is hosted in google app engine; development, staging and production. We already have example.com mapped to master version of app but I need to map staging.extra.example.com to staging environment with ssl enabled. Google App Engine allows you to add a wildcard custom domain then it automatically maps each versions as subdomains of it. So, in our case, if we add *.extra.example.com, google app engine will automatically map staging environment(version) to staging.extra.example.com.