Security: constant time sha comparison for mcp token, DRY

src/middleware.js

@@ -4,13 +4,6 @@ import { NextResponse } from "next/server";
 const authEnabled = Boolean(process.env.HOMEPAGE_AUTH_ENABLED);
 const authSecret = process.env.NEXTAUTH_SECRET || process.env.HOMEPAGE_AUTH_SECRET;
 
-function hasMcpToken(req) {
-  const token = process.env.HOMEPAGE_MCP_TOKEN;
-  if (!token) return false;
-
-  return req.headers.get("authorization") === `Bearer ${token}` || req.headers.get("x-homepage-mcp-token") === token;
-}
-
 export async function middleware(req) {
   // Check the Host header, if HOMEPAGE_ALLOWED_HOSTS is set
   const host = req.headers.get("host");
@@ -27,8 +20,10 @@ export async function middleware(req) {
     return NextResponse.json({ error: "Host validation failed. See logs for more details." }, { status: 400 });
   }
 
-  if (authEnabled && !new URL(req.url).pathname.startsWith("/api/healthcheck")) {
-    if (new URL(req.url).pathname === "/api/mcp" && hasMcpToken(req)) {
+  const pathname = new URL(req.url).pathname;
+  if (authEnabled && !pathname.startsWith("/api/healthcheck")) {
+    // The MCP API handler authorizes both bearer tokens and Homepage sessions.
+    if (pathname === "/api/mcp") {
       return NextResponse.next();
     }
 

src/middleware.test.js

@@ -131,15 +131,12 @@ describe("middleware", () => {
     expect(res).toEqual({ type: "next" });
   });
 
-  it("allows MCP requests with a bearer token when auth is enabled", async () => {
+  it("delegates MCP authorization to the API handler", async () => {
     process.env.HOMEPAGE_AUTH_ENABLED = "true";
     process.env.HOMEPAGE_AUTH_SECRET = "secret";
-    process.env.HOMEPAGE_MCP_TOKEN = "mcp-secret";
 
     const middleware = await loadMiddleware();
-    const res = await middleware(
-      createReq("localhost:3000", "http://localhost:3000/api/mcp", { authorization: "Bearer mcp-secret" }),
-    );
+    const res = await middleware(createReq("localhost:3000", "http://localhost:3000/api/mcp"));
 
     expect(getToken).not.toHaveBeenCalled();
     expect(NextResponse.next).toHaveBeenCalled();

src/utils/mcp/homepage-mcp.js

@@ -1,4 +1,5 @@
 import { existsSync, mkdirSync, readFileSync, writeFileSync } from "fs";
+import { createHash, timingSafeEqual } from "node:crypto";
 import { join } from "path";
 
 import yaml from "js-yaml";
@@ -61,6 +62,12 @@ function requiredToken() {
   return process.env.HOMEPAGE_MCP_TOKEN;
 }
 
+function tokenMatches(provided, expectedDigest) {
+  if (typeof provided !== "string") return false;
+  const providedDigest = createHash("sha256").update(provided, "utf8").digest();
+  return timingSafeEqual(providedDigest, expectedDigest);
+}
+
 function jsonRpcResult(id, result) {
   return { jsonrpc: "2.0", id, result };
 }
@@ -440,7 +447,9 @@ export function mcpTokenAuthorized(req) {
   if (!token) return false;
 
   const authHeader = req.headers.authorization;
-  return authHeader === `Bearer ${token}` || req.headers["x-homepage-mcp-token"] === token;
+  const bearerToken = typeof authHeader === "string" && authHeader.startsWith("Bearer ") ? authHeader.slice(7) : null;
+  const expectedDigest = createHash("sha256").update(token, "utf8").digest();
+  return tokenMatches(bearerToken, expectedDigest) || tokenMatches(req.headers["x-homepage-mcp-token"], expectedDigest);
 }
 
 export function handleMcpRequest(message) {

src/utils/mcp/homepage-mcp.test.js

@@ -626,5 +626,9 @@ describe("utils/mcp/homepage-mcp", () => {
     expect(mod.mcpTokenAuthorized({ headers: { authorization: "Bearer secret" } })).toBe(true);
     expect(mod.mcpTokenAuthorized({ headers: { "x-homepage-mcp-token": "secret" } })).toBe(true);
     expect(mod.mcpTokenAuthorized({ headers: { authorization: "Bearer wrong" } })).toBe(false);
+
+    process.env.HOMEPAGE_MCP_TOKEN = "é";
+    expect(mod.mcpTokenAuthorized({ headers: { authorization: "Bearer a" } })).toBe(false);
+    expect(mod.mcpTokenAuthorized({ headers: { authorization: "Bearer é" } })).toBe(true);
   });
 });