Is your feature request related to a problem? Please describe.
I received a notification from GCP alerting that SignBlob and SignJwt will be decommissioned and this library still using it.
Describe the solution you'd like
The alert recommends the change
both authentication methods on:
https://iam.googleapis.com
Instead, it should use: https://iamcredentials.googleapis.com
Describe alternatives you've considered
since google will discontinue these methods I have considered look for another library or build a new one
Additional context
I'm using the class Signer which is the one that has a dependency on these endpoints.