Worked on the pubky-core repository to enhance the User Authentication System by implementing robust HTTP error propagation for external service interactions. Leveraging Rust for backend development, the update ensured that non-2xx HTTP responses are now surfaced as explicit errors, reducing the risk of silent failures and improving the reliability of authentication workflows. The approach centered on improved error handling and API integration, using error_for_status to standardize response management. Additionally, a targeted code formatting update was applied to inner_send_auth_token, aligning with project standards without altering behavior. These changes collectively improved maintainability and paved the way for more resilient authentication processes.