Developed a PAC-based upstream proxy configuration feature for the Prinzhorn/mitmproxy repository, focusing on enhancing network routing flexibility in enterprise environments. The work centered on implementing upstream_pac.py, which enables mitmproxy to use a Proxy Auto-Configuration (PAC) file for dynamic upstream proxy selection. The solution included robust handling of PAC URLs and introduced a fallback mechanism to an alternate proxy when the PAC file resolves to a direct connection, ensuring reliable routing across diverse networks. Leveraging Python scripting and network programming skills, the developer also automated PAC server integration, streamlining deployment and reducing manual proxy configuration for users.