Secure MCP endpoint for LAN clients

.env.example

@@ -1,4 +1,5 @@
-# The service binds to localhost only. Set a token if your harness supports bearer auth.
+# Keep localhost for same-Mac clients. For LAN clients, set this to the Mac's LAN IP.
 MACMINI_MCP_HOST=127.0.0.1
 MACMINI_MCP_PORT=7331
+# Required whenever MACMINI_MCP_HOST is not loopback.
 # MACMINI_MCP_TOKEN=replace-with-a-long-random-token

README.md

@@ -35,7 +35,7 @@ npm run check
 npm run service:install
 ```
 
-The service endpoint is:
+The service defaults to a same-Mac endpoint:
 
 ```text
 http://127.0.0.1:7331/mcp
@@ -71,6 +71,21 @@ Service logs are stored in `.logs/`.
 For a harness that supports Streamable HTTP, configure the local MCP URL as
 `http://127.0.0.1:7331/mcp`.
 
+For a trusted local-network harness such as a Raspberry Pi, set
+`MACMINI_MCP_HOST` in `.env` to the Mac's LAN IP and set a strong
+`MACMINI_MCP_TOKEN`. Then configure the remote MCP client with:
+
+```text
+URL: http://<mac-lan-ip>:7331/mcp
+Authorization: Bearer <MACMINI_MCP_TOKEN>
+```
+
+Restart after changing `.env`:
+
+```sh
+npm run service:restart
+```
+
 For a harness that launches stdio servers, use:
 
 ```json
@@ -90,11 +105,11 @@ On first use of a Notes, Calendar, or Reminders tool, macOS may ask for
 Automation access for Node. Permit only the applications you want the server
 to control under **System Settings > Privacy & Security > Automation**.
 
-The HTTP service binds to `127.0.0.1` by default. To require bearer
-authentication even locally, create `.env` from `.env.example` and set
-`MACMINI_MCP_TOKEN`; clients must then send `Authorization: Bearer <token>`.
-Do not bind to a non-loopback address without enabling authentication and
-reviewing the tools first.
+The HTTP service binds to `127.0.0.1` by default. When configured to bind to a
+LAN address, it refuses to start without `MACMINI_MCP_TOKEN`; clients must send
+`Authorization: Bearer <token>`. This is HTTP bearer authentication on your
+local network, not encrypted transport. Use it only on a trusted LAN or put it
+behind a private encrypted network such as a VPN.
 
 ## Development
 

scripts/install-service.sh

@@ -47,5 +47,5 @@ launchctl enable "$DOMAIN/$LABEL"
 launchctl kickstart -k "$DOMAIN/$LABEL"
 
 echo "Installed $LABEL"
-echo "Endpoint: http://127.0.0.1:7331/mcp"
+echo "Endpoint: configured by .env (see the service log for the listening URL)"
 echo "Logs: $LOG_DIR"

src/config.js

@@ -14,9 +14,16 @@ export function getConfig() {
     throw new Error("MACMINI_MCP_PORT must be an integer between 1 and 65535.");
   }
 
-  return {
+  const config = {
     host: process.env.MACMINI_MCP_HOST || "127.0.0.1",
     port,
     token: process.env.MACMINI_MCP_TOKEN || "",
   };
+
+  const isLoopback = ["127.0.0.1", "::1", "localhost"].includes(config.host);
+  if (!isLoopback && !config.token) {
+    throw new Error("MACMINI_MCP_TOKEN is required when listening beyond localhost.");
+  }
+
+  return config;
 }

src/http.js

@@ -1,4 +1,5 @@
 import http from "node:http";
+import { timingSafeEqual } from "node:crypto";
 import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
 import { getConfig } from "./config.js";
 import { createMacMiniMcpServer } from "./server.js";
@@ -9,7 +10,10 @@ function authorized(request) {
   if (!config.token) {
     return true;
   }
-  return request.headers.authorization === `Bearer ${config.token}`;
+  const authorization = request.headers.authorization || "";
+  const expected = Buffer.from(`Bearer ${config.token}`);
+  const provided = Buffer.from(authorization);
+  return provided.length === expected.length && timingSafeEqual(provided, expected);
 }
 
 const service = http.createServer(async (request, response) => {