refactor old idtoken logic to use library instead of gcloud

[codyoss]

https://github.com/GoogleCloudPlatform/golang-samples/blob/22d8055a29603cf7f9e459522f7dbb5d70d726f8/internal/cloudrunci/gcloud.go#L96-L110

[Jeadie]

I'm looking to get some more hands-on practice in Golang codebases. If this is still relevant and needs cleanup, can you provide some more details about what is involved. If I understand correctly, it is replacing the gcloud call gcloud --quiet auth print-identity-token with a call from golang pkg cloud.google.com/go. Looking through the docs, I can't seem to find equivalent functionality.

[codyoss]

@Jeadie I have not looked into this too much, but I image the idtoken package could be used here.