GCP IAM API can have delayed propagation

[gw0]

Problem:
It seems there is a delay between when new GCP SA keys are generated (created on-demand using this Vault GCP secrets engine) and when they are accepted by other GCP services (like GCS). If your app attempts to use them before they are propagated, it fails.

Expected behaviour:
Of course one would expect GCP SA keys to be valid from the moment they are issued. But on the other hand, the GCP secrets engine should return either an error or valid credentials. The simplest solution would be to have a delay option to wait for a short time before it returns the credentials (i.e. 5 seconds should probably be enough), such that they have time to propagate.