E.g. create an app engine standard php72 app and perform a curl request to another app engine app. Note that the header X-Appengine-Inbound-Appid is not sent with the curl request.
The usual answer to this is to use URL fetch service - but I don't see this in php72 docs?
The header is added by the URLFetch service. As long as the service is not following redirects, it will add the X-Appengine-Inbound-Appid header automatically.
You can find more information in this documentation. [1]
[1] App Identity PHP API Overview: https://cloud.google.com/appengine/docs/standard/php/appidentity/#asserting_identity_to_other_app_engine_apps
