Developed backward-compatible support for untrusted TLS certificates in the fastly/go-fastly client, enabling smoother local testing workflows. The work introduced an allow_untrusted_root option to both CreateCustomTLSCertificateInput and UpdateCustomTLSCertificateInput, allowing developers to upload TLS certificates signed by untrusted certificate authorities specifically for local environments. This feature was implemented in Go and focused on backend development and SDK enhancement, with careful attention to API integration and TLS/SSL protocols. Comprehensive documentation updates accompanied the code changes, ensuring clarity for users adopting the new option. The solution reduced friction in local testing and expanded the flexibility of TLS-related test coverage for the client.