From 17740daaf5c04c2a0271de9e89931a210886a3a7 Mon Sep 17 00:00:00 2001
From: Felix Weinberger <fweinberger@anthropic.com>
Date: Thu, 12 Jun 2025 17:57:41 +0100
Subject: [PATCH] fix: address @jenn-newton comments

- Add authentication and origin validation middleware to /config endpoint
- Implement timing-safe token comparison using crypto.timingSafeEqual()
- Add config read to initial env setup s.t. /config call is authenticated
---
 client/src/App.tsx  | 12 +++++++++---
 server/src/index.ts | 32 ++++++++++++++++++++++++++++----
 2 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/client/src/App.tsx b/client/src/App.tsx
index c44a0e5f..8aca8697 100644
--- a/client/src/App.tsx
+++ b/client/src/App.tsx
@@ -63,6 +63,7 @@ import ToolsTab from "./components/ToolsTab";
 import { InspectorConfig } from "./lib/configurationTypes";
 import {
   getMCPProxyAddress,
+  getMCPProxyAuthToken,
   getInitialSseUrl,
   getInitialTransportType,
   getInitialCommand,
@@ -345,7 +346,13 @@ const App = () => {
   }, [sseUrl]);
 
   useEffect(() => {
-    fetch(`${getMCPProxyAddress(config)}/config`)
+    const headers: HeadersInit = {};
+    const proxyAuthToken = getMCPProxyAuthToken(config);
+    if (proxyAuthToken) {
+      headers['Authorization'] = `Bearer ${proxyAuthToken}`;
+    }
+    
+    fetch(`${getMCPProxyAddress(config)}/config`, { headers })
       .then((response) => response.json())
       .then((data) => {
         setEnv(data.defaultEnvironment);
@@ -359,8 +366,7 @@ const App = () => {
       .catch((error) =>
         console.error("Error fetching default environment:", error),
       );
-    // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, []);
+  }, [config]);
 
   useEffect(() => {
     rootsRef.current = roots;
diff --git a/server/src/index.ts b/server/src/index.ts
index c82227ac..a6ca2f42 100644
--- a/server/src/index.ts
+++ b/server/src/index.ts
@@ -19,7 +19,7 @@ import { Transport } from "@modelcontextprotocol/sdk/shared/transport.js";
 import express from "express";
 import { findActualExecutable } from "spawn-rx";
 import mcpProxy from "./mcpProxy.js";
-import { randomUUID, randomBytes } from "node:crypto";
+import { randomUUID, randomBytes, timingSafeEqual } from "node:crypto";
 
 const SSE_HEADERS_PASSTHROUGH = ["authorization"];
 const STREAMABLE_HTTP_HEADERS_PASSTHROUGH = [
@@ -120,14 +120,38 @@ const authMiddleware = (req: express.Request, res: express.Response, next: expre
     return next();
   }
 
-  const authHeader = req.headers.authorization;
-  if (!authHeader || authHeader !== `Bearer ${sessionToken}`) {
+  const sendUnauthorized = () => {
     res.status(401).json({ 
       error: "Unauthorized", 
       message: "Authentication required. Use the session token shown in the console when starting the server."
     });
+  };
+
+  const authHeader = req.headers.authorization;
+  if (!authHeader || !authHeader.startsWith('Bearer ')) {
+    sendUnauthorized();
     return;
   }
+
+  const providedToken = authHeader.substring(7); // Remove 'Bearer ' prefix
+  const expectedToken = sessionToken;
+
+  // Convert to buffers for timing-safe comparison
+  const providedBuffer = Buffer.from(providedToken);
+  const expectedBuffer = Buffer.from(expectedToken);
+
+  // Check length first to prevent timing attacks
+  if (providedBuffer.length !== expectedBuffer.length) {
+    sendUnauthorized();
+    return;
+  }
+
+  // Perform timing-safe comparison
+  if (!timingSafeEqual(providedBuffer, expectedBuffer)) {
+    sendUnauthorized();
+    return;
+  }
+  
   next();
 };
 
@@ -444,7 +468,7 @@ app.get("/health", (req, res) => {
   });
 });
 
-app.get("/config", (req, res) => {
+app.get("/config", originValidationMiddleware, authMiddleware, (req, res) => {
   try {
     res.json({
       defaultEnvironment,