When deploying a background Cloud Function for Cloud Pub/Sub via:
gcloud functions deploy function_name --runtime python37 --trigger-topic some_topic
A subscription gets automatically created with a push endpoint (likely App Engine standard endpoint, but those are claimed to be without the need of domain verification https://cloud.google.com/pubsub/docs/push#other-endpoints).
For the generated subscription/endpoint there doesn't seem like a way to register/verify the domain (https://www.google.com/webmasters/verification, https://console.cloud.google.com/apis/credentials/domainverification)
As a result the user cannot alter the subscription, for instance:
gcloud alpha pubsub subscriptions update some_subscription --ack-deadline=10
Would yield something like "INVALID_ARGUMENT: The supplied HTTP URL is not registered in the subscription's parent project"
Doing it via the web interface on GCP would also yield an error: "pubsub error INVALID_ARGUMENT"
