Worked on Apache Kafka to enhance the reliability and security of authentication by implementing startup-time validation for the OAuthBearer server callback. This change ensures that the system now requires complete configuration at startup, immediately failing with a ConfigException if any configuration is missing, which prevents misconfiguration-driven authentication failures from reaching production. The solution was delivered as a focused patch with clear traceability and disciplined scope management. Utilizing Java and backend development skills with a strong emphasis on security, the work improved operability by surfacing configuration issues early, reducing production risk and supporting more robust deployment practices in the apache/kafka repository.