TL;DR: an LLM that calls tools is a client you cannot trust. And it holds your production credentials. The most important rule fits in one sentence. Your server decides who the user is, never the model. In this article, I show how I secured a real LLM agent in Go, in production. Everything also applies to MCP servers.
This article is for Go developers who put an LLM agent or an MCP server in production. Not in a demo.
Everyone builds MCP servers. Almost nobody secures them.
MCP stands for Model Context Protocol. It is a standard that lets an AI use your tools: read a file, call an API, query a database. Everyone is adopting it, fast. And building an MCP server in Go is easy. Twenty lines are enough with the official SDK:
package main
