Add policy-based authorization to your FastMCP servers with one-line code addition with the Eunomia authorization middleware. Control which tools, resources and prompts MCP clients can view and execute on your server. Define dynamic JSON-based policies and obtain a comprehensive audit log of all access attempts and violations.

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How it Works

Exploiting FastMCP’s Middleware, the Eunomia middleware intercepts all MCP requests to your server and automatically maps MCP methods to authorization checks.

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Listing Operations

The middleware behaves as a filter for listing operations (tools/list, resources/list, prompts/list), hiding to the client components that are not authorized by the defined policies.

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Execution Operations

The middleware behaves as a firewall for execution operations (tools/call, resources/read, prompts/get), blocking operations that are not authorized by the defined policies.

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Add Authorization to Your Server

Eunomia is an AI-specific authorization server that handles policy decisions. The server runs embedded within your MCP server by default for a zero-effort configuration, but can alternatively be run remotely for centralized policy decisions.

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Create a Server with Authorization

First, install the eunomia-mcp package: 
pip install eunomia-mcp
Then create a FastMCP server and add the Eunomia middleware in one line:
server.py
from fastmcp import FastMCP
from eunomia_mcp import create_eunomia_middleware

# Create your FastMCP server
mcp = FastMCP("Secure MCP Server 🔒")

@mcp.tool()
def add(a: int, b: int) -> int:
    """Add two numbers"""
    return a + b

# Add middleware to your server
middleware = create_eunomia_middleware(policy_file="mcp_policies.json")
mcp.add_middleware(middleware)

if __name__ == "__main__":
    mcp.run()

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Configure Access Policies

Use the eunomia-mcp CLI in your terminal to manage your authorization policies: 
# Create a default policy file
eunomia-mcp init

# Or create a policy file customized for your FastMCP server
eunomia-mcp init --custom-mcp "app.server:mcp"
This creates mcp_policies.json file that you can further edit to your access control needs. 
# Once edited, validate your policy file
eunomia-mcp validate mcp_policies.json

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Run the Server

Start your FastMCP server normally: 
python server.py
The middleware will now intercept all MCP requests and check them against your policies. Requests include agent identification through headers like X-Agent-ID, X-User-ID, User-Agent, or Authorization and an automatic mapping of MCP methods to authorization resources and actions.
For detailed policy configuration, custom authentication, and remote deployments, visit the Eunomia MCP Middleware repository.