modelcontextprotocol/inspector
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feat: add session token authentication to proxy server

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- Generate random session token on server startup using crypto.randomBytes
- Add authentication middleware requiring Bearer token for all sensitive endpoints
- Apply auth to /mcp, /stdio, /sse, and /message endpoints
- Display session token in console on startup
- Add DANGEROUSLY_OMIT_AUTH environment variable to disable auth for development
- Update README with authentication documentation

This prevents unauthorized access to the proxy server's ability to execute
local processes and connect to MCP servers.
This commit is contained in:
Felix Weinberger 2025-06-10 14:05:17 +01:00
commit 111e282386
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1 changed files with 66 additions and 7 deletions
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44
server/src/index.ts
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@ -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 } from "node:crypto";
import { randomUUID, randomBytes } from "node:crypto";
const SSE_HEADERS_PASSTHROUGH = ["authorization"];
const STREAMABLE_HTTP_HEADERS_PASSTHROUGH = [
@ -89,6 +89,25 @@ app.use((req, res, next) => {
const webAppTransports: Map<string, Transport> = new Map<string, Transport>(); // Web app transports by web app sessionId
const serverTransports: Map<string, Transport> = new Map<string, Transport>(); // Server Transports by web app sessionId
const sessionToken = randomBytes(32).toString('hex');
const authDisabled = !!process.env.DANGEROUSLY_OMIT_AUTH;
const authMiddleware = (req: express.Request, res: express.Response, next: express.NextFunction) => {
if (authDisabled) {
return next();
}
const authHeader = req.headers.authorization;
if (!authHeader || authHeader !== `Bearer ${sessionToken}`) {
res.status(401).json({
error: "Unauthorized",
message: "Authentication required. Use the session token shown in the console when starting the server."
});
return;
}
next();
};
const createTransport = async (req: express.Request): Promise<Transport> => {
const query = req.query;
console.log("Query parameters:", JSON.stringify(query));
@ -150,7 +169,7 @@ const createTransport = async (req: express.Request): Promise<Transport> => {
}
};
app.get("/mcp", async (req, res) => {
app.get("/mcp", authMiddleware, async (req, res) => {
const sessionId = req.headers["mcp-session-id"] as string;
console.log(`Received GET message for sessionId ${sessionId}`);
try {
@ -169,7 +188,7 @@ app.get("/mcp", async (req, res) => {
}
});
app.post("/mcp", async (req, res) => {
app.post("/mcp", authMiddleware, async (req, res) => {
const sessionId = req.headers["mcp-session-id"] as string | undefined;
let serverTransport: Transport | undefined;
if (!sessionId) {
@ -239,7 +258,7 @@ app.post("/mcp", async (req, res) => {
}
});
app.delete("/mcp", async (req, res) => {
app.delete("/mcp", authMiddleware, async (req, res) => {
const sessionId = req.headers["mcp-session-id"] as string | undefined;
console.log(`Received DELETE message for sessionId ${sessionId}`);
let serverTransport: Transport | undefined;
@ -266,7 +285,7 @@ app.delete("/mcp", async (req, res) => {
}
});
app.get("/stdio", async (req, res) => {
app.get("/stdio", authMiddleware, async (req, res) => {
try {
console.log("New STDIO connection request");
let serverTransport: Transport | undefined;
@ -328,7 +347,7 @@ app.get("/stdio", async (req, res) => {
}
});
app.get("/sse", async (req, res) => {
app.get("/sse", authMiddleware, async (req, res) => {
try {
console.log(
"New SSE connection request. NOTE: The sse transport is deprecated and has been replaced by StreamableHttp",
@ -377,7 +396,7 @@ app.get("/sse", async (req, res) => {
}
});
app.post("/message", async (req, res) => {
app.post("/message", authMiddleware, async (req, res) => {
try {
const sessionId = req.query.sessionId;
console.log(`Received POST message for sessionId ${sessionId}`);
@ -421,6 +440,17 @@ const HOST = process.env.HOST || '127.0.0.1';
const server = app.listen(PORT, HOST);
server.on("listening", () => {
console.log(`⚙️ Proxy server listening on ${HOST}:${PORT}`);
if (!authDisabled) {
console.log(`🔑 Session token: ${sessionToken}`);
console.log(`Use this token to authenticate requests or set DANGEROUSLY_OMIT_AUTH=true to disable auth`);
// Display clickable URL with pre-filled token
const clientPort = process.env.CLIENT_PORT || '6274';
const clientUrl = `http://localhost:${clientPort}/?MCP_PROXY_AUTH_TOKEN=${sessionToken}`;
console.log(`\n🔗 Open inspector with token pre-filled:\n ${clientUrl}`);
} else {
console.log(`⚠️ WARNING: Authentication is disabled. This is not recommended.`);
}
});
server.on("error", (err) => {
if (err.message.includes(`EADDRINUSE`)) {