Worked on the TUM-DSE/doctor-cluster-config repository to enhance user access management and security within a Nix-based configuration management environment. Delivered features that centralized user provisioning by consolidating user definitions and SSH key management, reducing duplication and simplifying onboarding processes. Focused on improving security posture by migrating user SSH keys to the ED25519 standard, aligning with modern cryptographic practices and minimizing operational impact. Leveraged skills in DevOps, system administration, and Nix to ensure consistent access control and maintainability. The work emphasized traceability and compatibility, with all changes scoped to user management and security hardening without affecting broader system behavior.