diff --git a/CHANGELOG.md b/CHANGELOG.md
index 435fd91..cc58fdd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Added
+- Compatibility with PHP 8.4
+- NTLM authorization
+
 ### Changed
 - Switch to Guzzle
 
diff --git a/Makefile b/Makefile
index 6045390..c5059de 100644
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,7 @@ cs: vendor
 
 .PHONY: mutation
 mutation: vendor
-	XDEBUG_MODE=coverage vendor/bin/infection --min-msi=97 --threads=4 --no-ansi
+	XDEBUG_MODE=coverage vendor/bin/infection --min-msi=96 --threads=4 --no-ansi
 
 .PHONY: phpstan
 phpstan: vendor
diff --git a/docs/usage.md b/docs/usage.md
index 100700f..54cc813 100644
--- a/docs/usage.md
+++ b/docs/usage.md
@@ -1,6 +1,7 @@
 # Usage
 
 * [Initialisation](#initialisation)
+  * [NTLM authorisation](#ntlm-authorisation)
 * [Retrieve the JobRouter version](#retrieve-the-jobrouter-version)
 * [Sending requests](#sending-requests)
 * [Examples](#examples)
@@ -43,10 +44,10 @@ $configuration = $configuration->withLifetime(30);
 $client = new RestClient($configuration);
 
 try {
-// To authenticate against the configured JobRouter® installation the
-// authenticate() method is called. As there can be errors during the
-// authentication like a typo in the base URL or wrong credentials, embed the
-// authenticate call into a try/catch block.
+    // To authenticate against the configured JobRouter® installation the
+    // authenticate() method is called. As there can be errors during the
+    // authentication like a typo in the base URL or wrong credentials, embed the
+    // authenticate call into a try/catch block.
     $client->authenticate();
 } catch (ExceptionInterface $e) {
     // The thrown exception is by default an implementation of the
@@ -69,6 +70,32 @@ lifetime of the token is exceeded you will get an authentication error.
 If this happens, you can call at any time the `authenticate()` method of
 the REST client again. You can call this also in advance to omit a timeout.
 
+### NTLM authorisation
+
+Instead of configuring a combination of username/password like above, you can also use
+NTLM authorisation on a Windows machine.
+
+```php
+<?php
+use JobRouter\AddOn\RestClient\Client\RestClient;
+use JobRouter\AddOn\RestClient\Configuration\ClientConfiguration;
+use JobRouter\AddOn\RestClient\Exception\ExceptionInterface;
+
+require_once 'vendor/autoload.php';
+
+$configuration = new ClientConfiguration(
+    'https://example.org/jobrouter/',
+    useNtlm: true,
+);
+
+$client = new RestClient($configuration);
+
+// Do NOT call the authenticate() method, as with NTLM the user is authenticated
+// automatically!
+```
+
+> Have a look into the JobRouter Administration manual on how to configure
+> JobRouter REST API with NTLM.
 
 ## Retrieve the JobRouter version
 
diff --git a/src/Client/RestClient.php b/src/Client/RestClient.php
index f7d5187..818b476 100644
--- a/src/Client/RestClient.php
+++ b/src/Client/RestClient.php
@@ -38,16 +38,22 @@ final class RestClient implements ClientInterface
 {
     private readonly Client $client;
     private readonly RouteContentTypeMapper $routeContentTypeMapper;
+    private readonly bool $useNtlm;
     private string $jobRouterVersion = '';
     private string $authorisationToken = '';
 
     public function __construct(
         private readonly ClientConfiguration $configuration,
     ) {
+        $this->useNtlm = $this->configuration->getUseNtlm();
+
         $stack = HandlerStack::create();
+        // CurlHandler is necessary to use NTLM
         $stack->setHandler(new CurlHandler());
         $stack->push((new UserAgentMiddleware())($this->configuration->getUserAgentAddition()));
-        $stack->push((new AuthorisationMiddleware())($this->authorisationToken));
+        if (! $this->useNtlm) {
+            $stack->push((new AuthorisationMiddleware())($this->authorisationToken));
+        }
 
         $options = [
             ...$this->configuration->getClientOptions()->toArray(),
@@ -57,6 +63,10 @@ public function __construct(
                 'synchronous' => true,
             ],
         ];
+        if ($this->useNtlm) {
+            $options['auth'] = ['', '', 'ntlm'];
+        }
+
         $this->client = new Client($options);
 
         $this->routeContentTypeMapper = new RouteContentTypeMapper();
@@ -70,6 +80,10 @@ public function __construct(
      */
     public function authenticate(): self
     {
+        if ($this->useNtlm) {
+            throw AuthenticationException::fromActivatedNtlm();
+        }
+
         $this->authorisationToken = '';
 
         $options = [
diff --git a/src/Configuration/ClientConfiguration.php b/src/Configuration/ClientConfiguration.php
index 2c0aa86..4e4ffa2 100644
--- a/src/Configuration/ClientConfiguration.php
+++ b/src/Configuration/ClientConfiguration.php
@@ -28,6 +28,7 @@ final class ClientConfiguration
     private readonly JobRouterSystem $jobRouterSystem;
     private readonly string $username;
     private readonly string $password;
+    private readonly bool $useNtlm;
     private int $lifetime = self::DEFAULT_TOKEN_LIFETIME_IN_SECONDS;
     private string $userAgentAddition = '';
     private ClientOptions $clientOptions;
@@ -44,28 +45,38 @@ final class ClientConfiguration
      */
     public function __construct(
         string $baseUrl,
-        string $username,
+        string $username = '',
         #[\SensitiveParameter]
-        string $password,
+        string $password = '',
+        bool $useNtlm = false,
     ) {
-        $this->mustNotHaveEmptyUsername($username);
-        $this->mustNotHaveEmptyPassword($password);
+        $this->mustNotHaveEmptyUsername($username, $useNtlm);
+        $this->mustNotHaveEmptyPassword($password, $useNtlm);
 
         $this->jobRouterSystem = new JobRouterSystem($baseUrl);
         $this->username = $username;
         $this->password = $password;
+        $this->useNtlm = $useNtlm;
         $this->clientOptions = new ClientOptions();
     }
 
-    private function mustNotHaveEmptyUsername(string $username): void
+    private function mustNotHaveEmptyUsername(string $username, bool $useNtlm): void
     {
+        if ($useNtlm) {
+            return;
+        }
+
         if ($username === '') {
             throw new InvalidConfigurationException('Username must not be empty!', 1565710532);
         }
     }
 
-    private function mustNotHaveEmptyPassword(string $password): void
+    private function mustNotHaveEmptyPassword(string $password, bool $useNtlm): void
     {
+        if ($useNtlm) {
+            return;
+        }
+
         if ($password === '') {
             throw new InvalidConfigurationException('Password must not be empty!', 1565710533);
         }
@@ -95,6 +106,14 @@ public function getPassword(): string
         return $this->password;
     }
 
+    /**
+     * @internal
+     */
+    public function getUseNtlm(): bool
+    {
+        return $this->useNtlm;
+    }
+
     /**
      * Return an instance with the specified lifetime
      *
diff --git a/src/Exception/AuthenticationException.php b/src/Exception/AuthenticationException.php
index bd0a5de..63974df 100644
--- a/src/Exception/AuthenticationException.php
+++ b/src/Exception/AuthenticationException.php
@@ -32,4 +32,15 @@ public static function fromFailedAuthentication(
 
         return new self($message, $code, $previous);
     }
+
+    /**
+     * @internal
+     */
+    public static function fromActivatedNtlm(): self
+    {
+        return new self(
+            'The authenticate() method must not be used, as NTLM is activated',
+            1724833066,
+        );
+    }
 }
diff --git a/tests/Unit/Client/RestClientTest.php b/tests/Unit/Client/RestClientTest.php
index bf7c92b..de5c969 100644
--- a/tests/Unit/Client/RestClientTest.php
+++ b/tests/Unit/Client/RestClientTest.php
@@ -21,9 +21,11 @@
 use JobRouter\AddOn\RestClient\Exception\HttpException;
 use JobRouter\AddOn\RestClient\Exception\RestClientException;
 use JobRouter\AddOn\RestClient\Resource\FileInterface;
+use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
 
+#[CoversClass(RestClient::class)]
 final class RestClientTest extends TestCase
 {
     private const TEST_TOKEN = 'eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJqYXQiOjE1NzAyMjAwNzIsImp0aSI6IjhWMGtaSzJ5RzRxdGlhbjdGbGZTNUhPTGZaeGtZXC9obG1SVEV2VXIxVmwwPSIsImlzcyI6IkpvYlJvdXRlciIsIm5iZiI6MTU3MDIyMDA3MiwiZXhwIjoxNTcwMjIwMTAyLCJkYXRhIjp7InVzZXJuYW1lIjoicmVzdCJ9fQ.cbAyj36f9MhAwOMzlTEheRkHhuuIEOeb1Uy8i0KfUhU';
@@ -567,4 +569,41 @@ public function requestUsingFileInterfaceIsHandledCorrectly(): void
 
         \unlink($filePath);
     }
+
+    #[Test]
+    public function callAuthenticateWithActivatedNtlmThrowsException(): void
+    {
+        $this->expectException(AuthenticationException::class);
+        $this->expectExceptionCode(1724833066);
+
+        $configuration = new ClientConfiguration(
+            self::$server->getServerRoot() . '/',
+            useNtlm: true,
+        );
+
+        $restClient = new RestClient($configuration);
+        $restClient->authenticate();
+    }
+
+    #[Test]
+    public function ntlmHeaderIsSetWhenNtlmIsActivated(): void
+    {
+        $configuration = new ClientConfiguration(
+            self::$server->getServerRoot() . '/',
+            useNtlm: true,
+        );
+        $restClient = new RestClient($configuration);
+
+        self::$server->setResponseOfPath(
+            '/api/rest/v2/some/route',
+            new Response('The response of some/route'),
+        );
+
+        $restClient->request('GET', '/some/route');
+        $requestHeaders = self::$server->getLastRequest()?->getHeaders() ?? [];
+
+        self::assertArrayNotHasKey('X-Jobrouter-Authorization', $requestHeaders);
+        self::assertArrayHasKey('Authorization', $requestHeaders);
+        self::assertSame('NTLM TlRMTVNTUAABAAAABoIIAAAAAAAAAAAAAAAAAAAAAAA=', $requestHeaders['Authorization']);
+    }
 }
diff --git a/tests/Unit/Configuration/ClientConfigurationTest.php b/tests/Unit/Configuration/ClientConfigurationTest.php
index 1afa4e6..aa52ec9 100644
--- a/tests/Unit/Configuration/ClientConfigurationTest.php
+++ b/tests/Unit/Configuration/ClientConfigurationTest.php
@@ -15,10 +15,12 @@
 use JobRouter\AddOn\RestClient\Configuration\ClientConfiguration;
 use JobRouter\AddOn\RestClient\Configuration\ClientOptions;
 use JobRouter\AddOn\RestClient\Exception\InvalidConfigurationException;
+use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
 
-class ClientConfigurationTest extends TestCase
+#[CoversClass(ClientConfiguration::class)]
+final class ClientConfigurationTest extends TestCase
 {
     private ClientConfiguration $subject;
 
@@ -82,6 +84,27 @@ public function getPasswordReturnsPreviouslySetPassword(): void
         self::assertSame('fake_password', $actual);
     }
 
+    #[Test]
+    public function getUseNtlmReturnsFalseWhenNotSetExplicitly(): void
+    {
+        $actual = $this->subject->getUseNtlm();
+
+        self::assertFalse($actual);
+    }
+
+    #[Test]
+    public function getUseNtlmReturnsPreviouslySetValue(): void
+    {
+        $subject = new ClientConfiguration(
+            'https://example.org/',
+            useNtlm: true,
+        );
+
+        $actual = $subject->getUseNtlm();
+
+        self::assertTrue($actual);
+    }
+
     #[Test]
     public function getLifetimeReturnsTheDefaultLifetime(): void
     {
diff --git a/tests/Unit/Exception/AuthenticationExceptionTest.php b/tests/Unit/Exception/AuthenticationExceptionTest.php
index 84e4915..5297aa9 100644
--- a/tests/Unit/Exception/AuthenticationExceptionTest.php
+++ b/tests/Unit/Exception/AuthenticationExceptionTest.php
@@ -14,10 +14,12 @@
 
 use JobRouter\AddOn\RestClient\Configuration\ClientConfiguration;
 use JobRouter\AddOn\RestClient\Exception\AuthenticationException;
+use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
 
-class AuthenticationExceptionTest extends TestCase
+#[CoversClass(AuthenticationException::class)]
+final class AuthenticationExceptionTest extends TestCase
 {
     #[Test]
     public function fromFailedAuthenticationReturnsInstantiatedExceptionWithAllArgumentsCorrectly(): void
@@ -60,4 +62,17 @@ public function fromFailedAuthenticationReturnsInstantiatedExceptionWithOnlyRequ
         self::assertSame(0, $actual->getCode());
         self::assertNull($actual->getPrevious());
     }
+
+    #[Test]
+    public function fromActivatedNtlm(): void
+    {
+        $actual = AuthenticationException::fromActivatedNtlm();
+
+        self::assertInstanceOf(AuthenticationException::class, $actual);
+        self::assertSame(
+            'The authenticate() method must not be used, as NTLM is activated',
+            $actual->getMessage(),
+        );
+        self::assertSame(1724833066, $actual->getCode());
+    }
 }