fix(dashboard): return timingSafeEqual result instead of discarding it

The unequal-length branch of timingSafeCompare called
crypto.timingSafeEqual(paddedA, paddedB) but did not capture the return
value, unconditionally returning false and leaving the timing-safe
comparison as dead code.

Adds a regression test covering shorter, longer, and exact-match
credential lengths to lock in the correct behaviour.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

src/dashboard.mjs

@@ -26,8 +26,7 @@ function timingSafeCompare(a, b) {
     const paddedB = Buffer.alloc(maxLen);
     bufA.copy(paddedA);
     bufB.copy(paddedB);
-    crypto.timingSafeEqual(paddedA, paddedB);
-    return false;
+    return crypto.timingSafeEqual(paddedA, paddedB);
   }
   return crypto.timingSafeEqual(bufA, bufB);
 }

test/dashboard-auth.test.mjs

@@ -88,6 +88,48 @@ test('Dashboard Authentication', async (t) => {
     }
   });
 
+  await t.test('returns 401 when password has different byte length than stored credential', async () => {
+    // Regression test for timingSafeCompare: previously the comparison result
+    // was discarded and `false` was returned unconditionally for unequal-length
+    // inputs, making the timing-safe branch dead code. Verify that a prefix of
+    // the correct password (shorter) and an extended version (longer) are both
+    // rejected.
+    process.env.TORCH_DASHBOARD_AUTH = 'admin:secret';
+    _resetTorchConfigCache();
+
+    server = await cmdDashboard(0);
+    testPort = server.address().port;
+
+    try {
+      const makeRequest = (credentials) => {
+        const auth = Buffer.from(credentials).toString('base64');
+        return new Promise((resolve) => {
+          http.get({
+            host: '127.0.0.1',
+            port: testPort,
+            path: '/dashboard/',
+            headers: { 'Authorization': `Basic ${auth}` }
+          }, resolve);
+        });
+      };
+
+      // Shorter than correct password — different byte length
+      const resShorter = await makeRequest('admin:secre');
+      assert.strictEqual(resShorter.statusCode, 401, 'shorter password must be rejected');
+
+      // Longer than correct password — different byte length
+      const resLonger = await makeRequest('admin:secret_extra');
+      assert.strictEqual(resLonger.statusCode, 401, 'longer password must be rejected');
+
+      // Correct credentials still work
+      const resCorrect = await makeRequest('admin:secret');
+      assert.notStrictEqual(resCorrect.statusCode, 401, 'correct credentials must not be rejected');
+    } finally {
+      delete process.env.TORCH_DASHBOARD_AUTH;
+      _resetTorchConfigCache();
+    }
+  });
+
   await t.test('returns 200 when auth is disabled', async () => {
     delete process.env.TORCH_DASHBOARD_AUTH;
     _resetTorchConfigCache();