Update from Google status page:
We're still actively working to resolve issues with Identity/Authentication. Future updates will follow when there is significant progress to report.
To summarize; some long-lived OAuth tokens have inadvertently been invalidated. This may affect the following Cloud services and will manifest as authentication errors:
Cloud APIs using OAuth tokens, and related services that use them
gcloud SDK
Cloud Storage gsutil
Cloud Dataflow
Note: not all customers are affected by this.
OAuth tokens may be recreated by running the following commands:
$ gcloud auth application-default login
$ gcloud auth login