public class ClientCredentialsJWTBearerTokenFlow
Authorizes new Bearer Tokens at runtime by authorizing claims needed for the http request.
This maintains a time-based Bearer Token cache. By default expires after 59 minutes
(the maximum time a token is valid is 60 minutes).
This cache and expiry period is system-wide and does not attend to per-instance expiry time
(e.g. "expires_in" from Google Compute -- which is set to the standard 3600 seconds).