fix(webauthn): tolerate zero-counter authenticators + recheck 2FA on register

- Swap the strict counter checker for a zero-tolerant one so platform
  authenticators / synced passkeys (which always report counter 0) can assert,
  while non-zero counters still must strictly increase (clone detection).
- Guard registration (options + register) and the UI on hasTwoFactorEnabled, so a
  key is never created against a disabled/reset second factor.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/Livewire/Settings/WebauthnKeys.php

@@ -17,7 +17,7 @@ class WebauthnKeys extends Component
     /** JSON creation options for navigator.credentials.create (the JS posts the result to register). */
     public function options(WebauthnService $webauthn): array
     {
-        abort_unless($webauthn->available(), 404);
+        abort_unless($webauthn->available() && Auth::user()->hasTwoFactorEnabled(), 404);
         // Validate the label BEFORE the browser ceremony, so an invalid name never
         // leaves an orphaned credential on the authenticator.
         $this->validate();
@@ -27,7 +27,9 @@ class WebauthnKeys extends Component
 
     public function register(array $attestation, WebauthnService $webauthn): void
     {
-        abort_unless($webauthn->available(), 404);
+        // Re-check 2FA enrollment (it may have been disabled in another tab since the
+        // ceremony started) so a key is never created against a reset second factor.
+        abort_unless($webauthn->available() && Auth::user()->hasTwoFactorEnabled(), 404);
         $this->validate();
 
         $cred = $webauthn->verifyRegistration(Auth::user(), $attestation, trim($this->newName));
@@ -92,7 +94,7 @@ class WebauthnKeys extends Component
     public function render()
     {
         return view('livewire.settings.webauthn-keys', [
-            'available' => app(WebauthnService::class)->available(),
+            'available' => app(WebauthnService::class)->available() && Auth::user()->hasTwoFactorEnabled(),
             'keys' => Auth::user()->webauthnCredentials()->latest()->get(),
         ]);
     }

app/Services/WebauthnService.php

@@ -4,6 +4,7 @@ namespace App\Services;
 
 use App\Models\User;
 use App\Models\WebauthnCredential;
+use App\Support\Webauthn\ZeroTolerantCounterChecker;
 use Throwable;
 use Webauthn\AttestationStatement\AttestationStatementSupportManager;
 use Webauthn\AttestationStatement\NoneAttestationStatementSupport;
@@ -174,10 +175,12 @@ class WebauthnService
 
     private function ceremony(): CeremonyStepManagerFactory
     {
-        // Defaults already register ES256+RS256, NoneAttestation and a strict counter
-        // checker; we only constrain the allowed origin to https://<rpId>.
+        // Defaults register ES256+RS256 + NoneAttestation; constrain the origin to
+        // https://<rpId> and swap the strict counter checker for a zero-tolerant one
+        // (platform authenticators / passkeys always report counter 0).
         $factory = new CeremonyStepManagerFactory;
         $factory->setAllowedOrigins(['https://'.$this->rpId()]);
+        $factory->setCounterChecker(new ZeroTolerantCounterChecker);
 
         return $factory;
     }

app/Support/Webauthn/ZeroTolerantCounterChecker.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace App\Support\Webauthn;
+
+use RuntimeException;
+use Webauthn\Counter\CounterChecker;
+use Webauthn\CredentialRecord;
+
+/**
+ * Counter check that tolerates authenticators which don't support a signature counter
+ * (platform authenticators / synchronized passkeys always report 0): a current counter
+ * of 0 is accepted, while a non-zero counter must strictly increase — keeping the
+ * cloned-authenticator / rollback detection for keys that do count.
+ */
+class ZeroTolerantCounterChecker implements CounterChecker
+{
+    public function check(CredentialRecord $credentialRecord, int $currentCounter): void
+    {
+        if ($currentCounter === 0) {
+            return; // counter unsupported by this authenticator
+        }
+
+        if ($currentCounter <= $credentialRecord->counter) {
+            throw new RuntimeException('Invalid WebAuthn signature counter (possible cloned authenticator).');
+        }
+    }
+}

tests/Feature/WebauthnKeysTest.php

@@ -16,7 +16,7 @@ class WebauthnKeysTest extends TestCase
 
     public function test_register_stores_credential(): void
     {
-        $user = User::factory()->create();
+        $user = User::factory()->create(['two_factor_secret' => 'x', 'two_factor_confirmed_at' => now()]);
         $this->actingAs($user);
         $svc = $this->mock(WebauthnService::class);
         $svc->shouldReceive('available')->andReturn(true);
@@ -34,7 +34,7 @@ class WebauthnKeysTest extends TestCase
 
     public function test_options_validate_label_before_ceremony(): void
     {
-        $user = User::factory()->create();
+        $user = User::factory()->create(['two_factor_secret' => 'x', 'two_factor_confirmed_at' => now()]);
         $this->actingAs($user);
         $this->mock(WebauthnService::class)->shouldReceive('available')->andReturn(true);