Protocol used to provide authorization tokens for gRPC calls. These tokens give access to the Fleet Engine service accounts.

The implementation should ensure that a valid authorization token is always available. The authorization token should have a minimum lifetime of 5 minutes to allow for requests to complete. Therefore, the authorization token must automatically renew expiring tokens and minimize the number of token refreshes by re-using a token until its lifetime nears its end.

Implementations of this protocol must be thread-safe.

Protocol for responding to periodic vehicle updates sent by GMTDVehicleReporter.