Starting July 1, 2021, calls to SignBlob and SignJwt (also known as JSON Web Tokens (JWT)) on the IAM API will no longer be supported and may fail.
Google is deprecating both authentication methods on: https://iam.googleapis.com Instead, we can now use: https://iamcredentials.googleapis.com
We must migrate our projects off the IAM API to the new IAMCredentials API to avoid a service disruption. The IAMCredentials API supports higher traffic volumes across the network, giving you better access and reliability.