fix(auth): race-safe first-run setup + rolling cookie max-age refresh

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/web/api/session.ts

@@ -2,10 +2,9 @@ import { Router } from "express";
 import type { Request, Response, NextFunction } from "express";
 import type { Logger } from "../../logger.js";
 import type { UserStore } from "../../data/users.js";
-import { UsernameTakenError } from "../../data/users.js";
 import type { SessionStore } from "../../data/sessions.js";
 import { SESSION_TTL_MS } from "../../data/sessions.js";
-import { SESSION_COOKIE_NAME, validateSessionFromHeaders } from "../auth/validateSession.js";
+import { SESSION_COOKIE_NAME, validateSessionFromHeaders, extractSessionToken } from "../auth/validateSession.js";
 
 const FAILED_LOGIN_DELAY_MS = 250;
 
@@ -60,6 +59,8 @@ export function createSessionRouter(
       return;
     }
     req.user = { id: result.userId, username: result.username };
+    const token = extractSessionToken(req.headers.cookie);
+    if (token) setSessionCookie(res, token);
     next();
   };
 
@@ -78,16 +79,16 @@ export function createSessionRouter(
       return;
     }
     try {
-      const user = await users.createUser(username, password);
+      const user = await users.createFirstUser(username, password);
+      if (!user) {
+        res.status(409).json({ error: "already initialized" });
+        return;
+      }
       const { token } = sessions.createSession(user.id);
       setSessionCookie(res, token);
       logger.info({ userId: user.id, username }, "First admin created");
       res.json({ id: user.id, username: user.username });
     } catch (err) {
-      if (err instanceof UsernameTakenError) {
-        res.status(409).json({ error: "already initialized" });
-        return;
-      }
       logger.error({ err }, "setup failed");
       res.status(500).json({ error: "internal" });
     }

src/web/auth/validateSession.ts

@@ -17,6 +17,11 @@ export function validateSessionFromHeaders(
   return sessions.validateAndTouch(token);
 }
 
+export function extractSessionToken(rawCookieHeader: string | undefined): string | null {
+  if (!rawCookieHeader) return null;
+  return parseCookie(rawCookieHeader, SESSION_COOKIE_NAME);
+}
+
 function parseCookie(header: string, name: string): string | null {
   for (const part of header.split(";")) {
     const trimmed = part.trim();

src/web/middleware/requireAuth.test.ts

@@ -53,4 +53,16 @@ describe("requireAuth middleware", () => {
     expect(res.body.ok).toBe(true);
     expect(res.body.user.username).toBe("alice");
   });
+
+  it("rolls the cookie max-age forward on successful auth", async () => {
+    const res = await request(app)
+      .get("/protected")
+      .set("Cookie", `${SESSION_COOKIE_NAME}=${validToken}`);
+    expect(res.status).toBe(200);
+    const setCookieHeaders = res.headers["set-cookie"];
+    const arr = Array.isArray(setCookieHeaders) ? setCookieHeaders : setCookieHeaders ? [setCookieHeaders] : [];
+    const refreshed = arr.find((c) => c.startsWith(`${SESSION_COOKIE_NAME}=`));
+    expect(refreshed).toBeDefined();
+    expect(refreshed!).toMatch(/Max-Age=\d+/);
+  });
 });

src/web/middleware/requireAuth.ts

@@ -1,6 +1,11 @@
 import type { Request, Response, NextFunction, RequestHandler } from "express";
 import type { SessionStore } from "../../data/sessions.js";
-import { validateSessionFromHeaders, SESSION_COOKIE_NAME } from "../auth/validateSession.js";
+import { SESSION_TTL_MS } from "../../data/sessions.js";
+import {
+  validateSessionFromHeaders,
+  extractSessionToken,
+  SESSION_COOKIE_NAME,
+} from "../auth/validateSession.js";
 
 declare module "express-serve-static-core" {
   interface Request {
@@ -17,6 +22,16 @@ export function createRequireAuth(sessions: SessionStore): RequestHandler {
       return;
     }
     req.user = { id: result.userId, username: result.username };
+    const token = extractSessionToken(req.headers.cookie);
+    if (token) {
+      res.cookie(SESSION_COOKIE_NAME, token, {
+        httpOnly: true,
+        sameSite: "lax",
+        secure: req.secure,
+        path: "/",
+        maxAge: SESSION_TTL_MS,
+      });
+    }
     next();
   };
 }