diff --git a/.env b/.env
index 4fd8920..4f2ec8f 100644
--- a/.env
+++ b/.env
@@ -44,8 +44,8 @@ MAILJET_API_KEY=
 MAILJET_API_SECRET=
 MAILJET_API_BASE_URL=https://api.mailjet.com/v3/REST
 MAILJET_DEFAULT_LIST_ID=
-# Development default for HTTP Basic Auth password "secret"; override in production secrets.
-MAILJET_WEBHOOK_BASIC_PASSWORD_HASH='$2y$10$uCeNsfVsTkGhylniiZTtGuzs3TDhFr7k/V36w6kD4LWHWbHuleDpa'
+# Development default for HTTP Basic Auth password; override in production secrets.
+MAILJET_WEBHOOK_BASIC_PASSWORD=secret
 APP_NEWSLETTER_CONFIRMATION_TTL_HOURS=1
 
 APP_BPN_USER=
diff --git a/.env.test b/.env.test
index f1e0e07..9d63102 100644
--- a/.env.test
+++ b/.env.test
@@ -4,4 +4,4 @@ APP_SECRET='$ecretf0rt3st'
 SYMFONY_DEPRECATIONS_HELPER=999999
 PANTHER_APP_ENV=panther
 PANTHER_ERROR_SCREENSHOT_DIR=./var/error-screenshots
-MAILJET_WEBHOOK_BASIC_PASSWORD_HASH='$2y$10$uCeNsfVsTkGhylniiZTtGuzs3TDhFr7k/V36w6kD4LWHWbHuleDpa'
+MAILJET_WEBHOOK_BASIC_PASSWORD=secret
diff --git a/config/packages/security.yaml b/config/packages/security.yaml
index 6792363..a87c278 100644
--- a/config/packages/security.yaml
+++ b/config/packages/security.yaml
@@ -1,6 +1,7 @@
 security:
     # https://symfony.com/doc/current/security.html#registering-the-user-hashing-passwords
     password_hashers:
+        Symfony\Component\Security\Core\User\InMemoryUser: 'plaintext'
         Symfony\Component\Security\Core\User\PasswordAuthenticatedUserInterface: 'auto'
     # https://symfony.com/doc/current/security.html#loading-the-user-the-user-provider
     providers:
@@ -12,7 +13,7 @@ security:
             memory:
                 users:
                     mailjet:
-                        password: '%env(MAILJET_WEBHOOK_BASIC_PASSWORD_HASH)%'
+                        password: '%env(MAILJET_WEBHOOK_BASIC_PASSWORD)%'
                         roles: ['ROLE_MAILJET_WEBHOOK']
     firewalls:
         dev:
@@ -58,6 +59,7 @@ when@test:
             # important to generate secure password hashes. In tests however, secure hashes
             # are not important, waste resources and increase test times. The following
             # reduces the work factor to the lowest possible values.
+            Symfony\Component\Security\Core\User\InMemoryUser: 'plaintext'
             Symfony\Component\Security\Core\User\PasswordAuthenticatedUserInterface:
                 algorithm: auto
                 cost: 4 # Lowest possible value for bcrypt
diff --git a/docs/technical-documentation.md b/docs/technical-documentation.md
index c620349..e6a4c0a 100644
--- a/docs/technical-documentation.md
+++ b/docs/technical-documentation.md
@@ -1169,6 +1169,8 @@ php bin/console app:mailjet:newsletter-webhook deactivate
 Creates or deletes the Mailjet `unsub` callback for `POST /webhooks/mailjet/newsletter`.
 
 - Uses `APP_BASE_URL` by default and appends the webhook path.
+- The command prepends `mailjet:<password>@` to the URL before registering it with Mailjet.
+- Configure the plain password in `MAILJET_WEBHOOK_BASIC_PASSWORD`; Symfony uses it for the webhook firewall.
 - Pass `--url` to target a different full webhook URL.
 - `register` prints the API response payload so you can note the callback ID.
 - `remove` and `deactivate` require the callback ID returned by Mailjet.
diff --git a/src/Command/MailjetNewsletterWebhookCommand.php b/src/Command/MailjetNewsletterWebhookCommand.php
index 5a88b0f..7fb770d 100644
--- a/src/Command/MailjetNewsletterWebhookCommand.php
+++ b/src/Command/MailjetNewsletterWebhookCommand.php
@@ -26,6 +26,7 @@ final class MailjetNewsletterWebhookCommand extends Command
     private const string ACTION_REMOVE = 'remove';
     private const string ACTION_DEACTIVATE = 'deactivate';
     private const string EVENT_TYPE_UNSUBSCRIBE = 'unsub';
+    private const string WEBHOOK_BASIC_AUTH_USER = 'mailjet';
     private const string WEBHOOK_PATH = '/webhooks/mailjet/newsletter';
     private const int WEBHOOK_VERSION = 2;
 
@@ -33,6 +34,8 @@ final class MailjetNewsletterWebhookCommand extends Command
         private readonly MailjetApiClient $mailjetApiClient,
         #[Autowire('%env(APP_BASE_URL)%')]
         private readonly string $defaultBaseUrl,
+        #[Autowire('%env(MAILJET_WEBHOOK_BASIC_PASSWORD)%')]
+        private readonly string $basicAuthPassword,
         private readonly LoggerInterface $logger,
     ) {
         parent::__construct();
@@ -43,7 +46,7 @@ final class MailjetNewsletterWebhookCommand extends Command
         $this
             ->addArgument('action', InputArgument::REQUIRED, 'One of: register, remove, deactivate')
             ->addArgument('callback_id', InputArgument::OPTIONAL, 'Callback ID required for remove/deactivate')
-            ->addOption('url', null, InputOption::VALUE_REQUIRED, 'Override the webhook URL to register');
+            ->addOption('url', null, InputOption::VALUE_REQUIRED, 'Override the webhook URL to register before Basic Auth credentials are added');
     }
 
     protected function execute(InputInterface $input, OutputInterface $output): int
@@ -72,9 +75,10 @@ final class MailjetNewsletterWebhookCommand extends Command
     private function register(SymfonyStyle $io, mixed $overrideUrl): int
     {
         $webhookUrl = $this->resolveWebhookUrl($overrideUrl);
-        $payload = $this->mailjetApiClient->createEventCallbackUrl(self::EVENT_TYPE_UNSUBSCRIBE, $webhookUrl, self::WEBHOOK_VERSION);
+        $authenticatedWebhookUrl = $this->prependBasicAuth($webhookUrl);
+        $payload = $this->mailjetApiClient->createEventCallbackUrl(self::EVENT_TYPE_UNSUBSCRIBE, $authenticatedWebhookUrl, self::WEBHOOK_VERSION);
 
-        $io->success(sprintf('Created Mailjet newsletter webhook at %s.', $webhookUrl));
+        $io->success(sprintf('Created Mailjet newsletter webhook at %s.', $authenticatedWebhookUrl));
         $io->writeln($this->formatPayload($payload));
 
         return Command::SUCCESS;
@@ -115,6 +119,47 @@ final class MailjetNewsletterWebhookCommand extends Command
         return rtrim(trim($this->defaultBaseUrl), '/').self::WEBHOOK_PATH;
     }
 
+    private function prependBasicAuth(string $url): string
+    {
+        if ('' === trim($this->basicAuthPassword)) {
+            throw new \InvalidArgumentException('MAILJET_WEBHOOK_BASIC_PASSWORD is not configured.');
+        }
+
+        $parts = parse_url($url);
+        if (false === is_array($parts) || false === isset($parts['scheme'], $parts['host'])) {
+            throw new \InvalidArgumentException('The webhook URL is not valid.');
+        }
+
+        $host = $parts['host'];
+        if (false === str_starts_with($host, '[') && true === str_contains($host, ':')) {
+            $host = sprintf('[%s]', $host);
+        }
+
+        $authenticatedUrl = sprintf(
+            '%s://%s:%s@%s',
+            $parts['scheme'],
+            rawurlencode(self::WEBHOOK_BASIC_AUTH_USER),
+            rawurlencode($this->basicAuthPassword),
+            $host,
+        );
+
+        if (isset($parts['port'])) {
+            $authenticatedUrl .= sprintf(':%d', $parts['port']);
+        }
+
+        $authenticatedUrl .= $parts['path'] ?? '';
+
+        if (isset($parts['query'])) {
+            $authenticatedUrl .= '?'.$parts['query'];
+        }
+
+        if (isset($parts['fragment'])) {
+            $authenticatedUrl .= '#'.$parts['fragment'];
+        }
+
+        return $authenticatedUrl;
+    }
+
     private function resolveCallbackId(mixed $callbackId): int
     {
         if (true === is_int($callbackId) && $callbackId > 0) {
diff --git a/src/Controller/Webhook/MailjetNewsletterWebhookController.php b/src/Controller/Webhook/MailjetNewsletterWebhookController.php
index 1e991ca..13f33d3 100644
--- a/src/Controller/Webhook/MailjetNewsletterWebhookController.php
+++ b/src/Controller/Webhook/MailjetNewsletterWebhookController.php
@@ -22,7 +22,7 @@ final class MailjetNewsletterWebhookController extends AbstractController
     }
 
     #[Route('/webhooks/mailjet/newsletter', name: 'app_webhook_mailjet_newsletter', methods: ['POST'])]
-    public function __invoke(Request $request): JsonResponse
+    public function index(Request $request): JsonResponse
     {
         $payload = json_decode($request->getContent(), true);
         if (JSON_ERROR_NONE !== json_last_error() || false === is_array($payload)) {
@@ -51,8 +51,7 @@ final class MailjetNewsletterWebhookController extends AbstractController
     }
 
     /**
-     * @param array<mixed> $payload
-     *
+     * @param array<string, mixed> $payload
      * @return list<array<string, mixed>>
      */
     private function normalizeEvents(array $payload): array
diff --git a/tests/Command/MailjetNewsletterWebhookCommandTest.php b/tests/Command/MailjetNewsletterWebhookCommandTest.php
index 6761fb5..db3ce42 100644
--- a/tests/Command/MailjetNewsletterWebhookCommandTest.php
+++ b/tests/Command/MailjetNewsletterWebhookCommandTest.php
@@ -20,7 +20,7 @@ class MailjetNewsletterWebhookCommandTest extends TestCase
             ->method('createEventCallbackUrl')
             ->with(
                 'unsub',
-                'https://my.ep-reisen.de/webhooks/mailjet/newsletter',
+                'https://mailjet:secret@my.ep-reisen.de/webhooks/mailjet/newsletter',
                 2,
                 false,
             )
@@ -89,6 +89,7 @@ class MailjetNewsletterWebhookCommandTest extends TestCase
         return new MailjetNewsletterWebhookCommand(
             $mailjetApiClient,
             'https://my.ep-reisen.de',
+            'secret',
             $this->createMock(LoggerInterface::class),
         );
     }
diff --git a/tests/Controller/Webhook/MailjetNewsletterWebhookControllerTest.php b/tests/Controller/Webhook/MailjetNewsletterWebhookControllerTest.php
index 6a3edb4..81be6c7 100644
--- a/tests/Controller/Webhook/MailjetNewsletterWebhookControllerTest.php
+++ b/tests/Controller/Webhook/MailjetNewsletterWebhookControllerTest.php
@@ -29,7 +29,7 @@ class MailjetNewsletterWebhookControllerTest extends TestCase
             ->willReturnCallback(static fn (object $message): Envelope => new Envelope($message));
 
         $controller = new MailjetNewsletterWebhookController($messageBus, new NullLogger());
-        $response = $controller(Request::create(
+        $response = $controller->index(Request::create(
             '/webhooks/mailjet/newsletter',
             'POST',
             content: json_encode([
@@ -61,7 +61,7 @@ class MailjetNewsletterWebhookControllerTest extends TestCase
         $messageBus->expects(self::never())->method('dispatch');
 
         $controller = new MailjetNewsletterWebhookController($messageBus, new NullLogger());
-        $response = $controller(Request::create('/webhooks/mailjet/newsletter', 'POST', content: '{'));
+        $response = $controller->index(Request::create('/webhooks/mailjet/newsletter', 'POST', content: '{'));
 
         self::assertSame(400, $response->getStatusCode());
     }
@@ -72,7 +72,7 @@ class MailjetNewsletterWebhookControllerTest extends TestCase
         $messageBus->expects(self::never())->method('dispatch');
 
         $controller = new MailjetNewsletterWebhookController($messageBus, new NullLogger());
-        $response = $controller(Request::create(
+        $response = $controller->index(Request::create(
             '/webhooks/mailjet/newsletter',
             'POST',
             content: json_encode([