WIP: Simple tool to get tokens from K8S and GKE, debug
By default it returns a JWT issued by K8S with audience "istio-ca", suitable to use with Istiod for debug.
The audience can be customized using "-aud AUDIENCE" - typically should be the base URL of the service where the token is used.
Using "-fed" returns a federated token - i.e. a JWT signed by Google, authenticating the K8S SA directly.
Using "-gsa GSA" will return a JWT token for the GSA. "default" will use the ASM data plane service account.