Worked on security hardening for the DuendeSoftware/products repository, focusing on the OAuth authentication flow. Addressed a compliance issue by updating the redirect URI fragment behavior during error scenarios, replacing the deprecated '#_=_' fragment with a safer '#_' approach when no existing fragment is present. This targeted fix, implemented in C#, improved the security and reliability of OAuth 2 error handling, reducing the risk of token leakage and aligning the codebase with current OAuth 2 security recommendations. Leveraged backend development and security expertise to ensure the authentication flow remains robust, maintainable, and interoperable with modern OAuth clients and standards.