Don Kjer enhanced the spiffe/spire repository by developing a new selector for the Docker workload attestor, targeting image config digest to improve workload registration stability across mirrored registries. Working primarily in Go and leveraging Docker expertise, Don focused on increasing reliability and trust in workload identity for multi-registry environments. The technical approach involved a concise, well-documented code change that addressed registration failures by ensuring consistent selector behavior, even when images are mirrored. Don collaborated closely with other engineers, emphasizing code quality and maintainability. The work demonstrated depth in Go-based engineering and a strong understanding of testing and deployment reliability.