fix(auth): redirect active sessions from /login (#9491)

Validated in local merge-train (diegosouzapw batch)

changelog.d/fixes/9491-port-3005-auth-redirect-login.md

@@ -0,0 +1 @@
+- **fix(auth):** redirect active sessions from /login by checking the session cookie before showing the login form. (thanks @DaDecky)

src/app/api/settings/require-login/route.ts

@@ -1,4 +1,6 @@
 import { NextResponse } from "next/server";
+import { cookies } from "next/headers";
+import { jwtVerify } from "jose";
 import { getSettings, updateSettings } from "@/lib/localDb";
 import {
   hasManagementPasswordConfigured,
@@ -9,6 +11,24 @@ import { getNodeRuntimeSupport } from "@/shared/utils/nodeRuntimeSupport.ts";
 import { updateRequireLoginSchema } from "@/shared/validation/schemas";
 import { isValidationFailure, validateBody } from "@/shared/validation/helpers";
 
+function getJwtSecret(): Uint8Array | null {
+  const secret = process.env.JWT_SECRET?.trim();
+  return secret ? new TextEncoder().encode(secret) : null;
+}
+
+async function checkSessionAuthenticated(): Promise<boolean> {
+  try {
+    const cookieStore = await cookies();
+    const token = cookieStore.get("auth_token")?.value;
+    const secret = getJwtSecret();
+    if (!token || !secret) return false;
+    await jwtVerify(token, secret);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
 // Node.js compatibility check — reflect the supported secure runtime floors used by CLI/CI.
 function getNodeCompatibility() {
   const { nodeVersion, nodeCompatible } = getNodeRuntimeSupport();
@@ -28,10 +48,12 @@ export async function GET() {
   try {
     const settings = await getSettings();
     const requireLogin = settings.requireLogin !== false;
+    const authenticated = await checkSessionAuthenticated();
     const hasPassword = hasManagementPasswordConfigured(settings);
     const setupComplete = !!settings.setupComplete;
     const oidcEnabled = !!settings.oidcEnabled;
     return NextResponse.json({
+      authenticated,
       requireLogin,
       hasPassword,
       setupComplete,
@@ -42,6 +64,7 @@ export async function GET() {
     console.error("[API] Error fetching require-login settings:", error);
     return NextResponse.json(
       {
+        authenticated: false,
         requireLogin: true,
         hasPassword: true,
         setupComplete: true,

src/app/login/page.tsx

@@ -36,7 +36,7 @@ export default function LoginPage() {
           const data = await res.json();
           if (data.nodeVersion) setNodeVersion(data.nodeVersion);
           if (data.nodeCompatible === false) setNodeCompatible(false);
-          if (data.requireLogin === false) {
+          if (data.authenticated === true || data.requireLogin === false) {
             router.push("/dashboard");
             router.refresh();
             return;

tests/unit/auth-redirect-login.test.ts

@@ -0,0 +1,41 @@
+/**
+ * Auth redirect: active sessions are redirected from /login to /dashboard.
+ *
+ * Upstream: decolua/9router#3005 — fix(auth): redirect active sessions from /login
+ * When a user navigates to /login while already authenticated, the login page
+ * fetches /api/settings/require-login and redirects to /dashboard.
+ */
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import path from "node:path";
+
+describe("auth redirect login (port from 9router#3005)", () => {
+  it("login page checks data.authenticated === true before showing the form", () => {
+    const source = fs.readFileSync(path.resolve("src/app/login/page.tsx"), "utf-8");
+    // The redirect guard must check both:
+    //   - authenticated=true (active session → redirect to dashboard)
+    //   - requireLogin=false (no auth configured → allow access)
+    const redirectCheck = source.match(/if\s*\(.*authenticated.*requireLogin.*\)/);
+    assert.ok(redirectCheck, "login page must check both authenticated and requireLogin");
+    assert.ok(
+      source.includes("data.authenticated === true"),
+      "login page must check data.authenticated === true for redirect",
+    );
+  });
+
+  it("require-login API route returns authenticated field", () => {
+    const source = fs.readFileSync(
+      path.resolve("src/app/api/settings/require-login/route.ts"),
+      "utf-8",
+    );
+    assert.ok(
+      source.includes("authenticated:"),
+      "require-login route must include authenticated in the response",
+    );
+    assert.ok(
+      source.includes("authenticated,"),
+      "authenticated must be part of the JSON response object (spread or key)",
+    );
+  });
+});