gserviceaccount/opts.go
func Transport(transport http.RoundTripper) Option {
	return func(gsa *GServiceAccount) error {
		gsa.transport = transport
		return nil
	}
}
func Transport(transport http.RoundTripper) Option {
	return func(gsa *GServiceAccount) error {
		gsa.transport = transport
		return nil
	}
}
// Transport is a GServiceAccount option to set the client transport used by
// the token source.