Leon worked on the evcc-io/evcc repository, focusing on backend development and security improvements related to MQTT configuration management. He refactored the MQTT secrets handling by centralizing all related configuration into a single struct, streamlining how sensitive information is managed within the codebase. Using Go, Leon enhanced the redaction logic to ensure secrets are masked during configuration merges, effectively preventing accidental exposure in logs or the user interface. This approach not only reduced the risk of secret leakage but also improved the maintainability of the configuration system, demonstrating a thoughtful balance between security and long-term code organization within the project.