See also:
https://cloud.google.com/pubsub/access_control PubSub Access Control Documentation
See also:
https://cloud.google.com/pubsub/docs/reference/rest/v1/projects.subscriptions/getIamPolicy Get Subscription IAM Policy
See also:
https://cloud.google.com/pubsub/docs/reference/rest/v1/projects.subscriptions/setIamPolicy Set Subscription IAM Policy
See also:
https://cloud.google.com/pubsub/docs/reference/rest/v1/projects.subscriptions/testIamPermissions Test Subscription Permissions