Openresty

When applications interact with LLMs or MCP servers, every request and response is a potential attack surface. One way to add protection is to put a proxy at the edge, where you can inspect traffic and enforce security rules. Just as firewalls and WAFs shield web apps from SQL injection or XSS, a proxy can serve as an "AI firewall" to defend against risks like those in the OWASP Top 10 for LLMs. In this article, I will walk through how to build such a firewall using Nginx, OpenResty, and Lua.

A custom web application firewall (WAF) can help protect your web application from various threats like SQL injection, cross-site scripting (XSS), etc. If you ship software to customers or even if you host your services in the cloud but want more control, agility and/or simplicity, a custom WAF can help. In this article, I will show you how to build a custom WAF using OpenResty, a powerful web platform based on Nginx and Lua.