diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 34baf10..ecc05eb 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -32,4 +32,4 @@ jobs:
       os: >-
         ['ubuntu-latest', 'windows-latest']
       php: >-
-        ['8.1', '8.2', '8.3']
+        ['8.1', '8.2', '8.3', '8.4']
diff --git a/.github/workflows/composer-require-checker.yml b/.github/workflows/composer-require-checker.yml
index a857bce..a93390b 100644
--- a/.github/workflows/composer-require-checker.yml
+++ b/.github/workflows/composer-require-checker.yml
@@ -31,4 +31,4 @@ jobs:
       os: >-
         ['ubuntu-latest']
       php: >-
-        ['8.1', '8.2', '8.3']
+        ['8.1', '8.2', '8.3', '8.4']
diff --git a/.github/workflows/rector.yml b/.github/workflows/rector.yml
index 457772a..5d6931d 100644
--- a/.github/workflows/rector.yml
+++ b/.github/workflows/rector.yml
@@ -21,4 +21,4 @@ jobs:
       os: >-
         ['ubuntu-latest']
       php: >-
-        ['8.3']
+        ['8.4']
diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
index e33eca8..d03874d 100644
--- a/.github/workflows/static.yml
+++ b/.github/workflows/static.yml
@@ -29,4 +29,4 @@ jobs:
       os: >-
         ['ubuntu-latest']
       php: >-
-        ['8.1', '8.2', '8.3']
+        ['8.1', '8.2', '8.3', '8.4']
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7deb59f..5011689 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,9 @@
 
 - Chg #101: Rename `UserAuth` to `WebAuth`, mark `UserAuth` as deprecated (@olegbaturin)
 - New #101: Add `ApiAuth` authentication method (@olegbaturin)
+- Chg #109: Change PHP constraint in `composer.json` to `~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0` (@vjik)
+- Bug #109: Explicitly mark nullable parameters (@vjik)
+- Enh #109: Improve debug message "Unable to authenticate user…" in `LogginMiddleware` (@vjik) 
 
 ## 2.2.0 May 07, 2024
 
diff --git a/README.md b/README.md
index 264bc88..2fae34c 100644
--- a/README.md
+++ b/README.md
@@ -26,7 +26,6 @@ The package handles user-related functionality:
 ## Requirements
 
 - PHP 8.1 or higher.
-- `JSON` PHP extension.
 
 ## Installation
 
diff --git a/composer.json b/composer.json
index cfe49ae..bd0282d 100644
--- a/composer.json
+++ b/composer.json
@@ -27,30 +27,29 @@
         }
     ],
     "require": {
-        "php": "^8.1",
-        "ext-json": "*",
+        "php": "~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0",
         "psr/event-dispatcher": "^1.0",
-        "psr/http-message": "^1.0|^2.0",
+        "psr/http-message": "^1.0 || ^2.0",
         "psr/http-factory": "^1.0",
         "psr/http-server-handler": "^1.0",
         "psr/http-server-middleware": "^1.0",
-        "psr/log": "^1.1|^2.0|^3.0",
+        "psr/log": "^1.1 || ^2.0 || ^3.0",
         "yiisoft/access": "^2.0",
-        "yiisoft/auth": "^2.0|^3.0",
+        "yiisoft/auth": "^2.0 || ^3.0",
         "yiisoft/cookies": "^1.2",
-        "yiisoft/session": "^1.0|^2.0",
+        "yiisoft/session": "^1.0 || ^2.0",
         "yiisoft/http": "^1.2"
     },
     "require-dev": {
-        "httpsoft/http-message": "^1.0",
-        "maglnet/composer-require-checker": "^4.2",
-        "phpunit/phpunit": "^10.5",
-        "rector/rector": "^2.0.0",
-        "roave/infection-static-analysis-plugin": "^1.16",
-        "spatie/phpunit-watcher": "^1.23",
-        "vimeo/psalm": "^5.23",
-        "yiisoft/di": "^1.0",
-        "yiisoft/test-support": "^3.0"
+        "httpsoft/http-message": "^1.1.6",
+        "maglnet/composer-require-checker": "^4.7.1",
+        "phpunit/phpunit": "^10.5.45",
+        "rector/rector": "^2.0.9",
+        "roave/infection-static-analysis-plugin": "^1.35",
+        "spatie/phpunit-watcher": "^1.24",
+        "vimeo/psalm": "^5.26.1 || ^6.8.6",
+        "yiisoft/di": "^1.3",
+        "yiisoft/test-support": "^3.0.2"
     },
     "autoload": {
         "psr-4": {
@@ -73,6 +72,7 @@
     },
     "config": {
         "sort-packages": true,
+        "bump-after-update": "dev",
         "allow-plugins": {
             "infection/extension-installer": true,
             "composer/package-versions-deprecated": true
diff --git a/psalm.xml b/psalm.xml
index 73ed715..44f8eab 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -3,6 +3,8 @@
     errorLevel="1"
     findUnusedBaselineEntry="true"
     findUnusedCode="false"
+    ensureOverrideAttribute="false"
+    strictBinaryOperands="false"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="https://getpsalm.org/schema/config"
     xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
diff --git a/rector.php b/rector.php
index 137e59d..8a9320a 100644
--- a/rector.php
+++ b/rector.php
@@ -5,6 +5,7 @@
 use Rector\CodeQuality\Rector\Class_\InlineConstructorDefaultToPropertyRector;
 use Rector\Config\RectorConfig;
 use Rector\Php74\Rector\Closure\ClosureToArrowFunctionRector;
+use Rector\Php81\Rector\ClassMethod\NewInInitializerRector;
 use Rector\Php81\Rector\Property\ReadOnlyPropertyRector;
 use Rector\Php81\Rector\FuncCall\NullToStrictStringFuncCallArgRector;
 use Rector\Set\ValueObject\LevelSetList;
@@ -27,5 +28,6 @@
         ClosureToArrowFunctionRector::class,
         ReadOnlyPropertyRector::class,
         NullToStrictStringFuncCallArgRector::class,
+        NewInInitializerRector::class,
     ]);
 };
diff --git a/src/CurrentUser.php b/src/CurrentUser.php
index 3258807..45d3230 100644
--- a/src/CurrentUser.php
+++ b/src/CurrentUser.php
@@ -42,7 +42,7 @@ final class CurrentUser
     public function __construct(
         private IdentityRepositoryInterface $identityRepository,
         private EventDispatcherInterface $eventDispatcher,
-        GuestIdentityFactoryInterface $guestIdentityFactory = null
+        ?GuestIdentityFactoryInterface $guestIdentityFactory = null
     ) {
         $this->guestIdentityFactory = $guestIdentityFactory ?? new GuestIdentityFactory();
     }
diff --git a/src/Login/LoginMiddleware.php b/src/Login/LoginMiddleware.php
index 633ef93..5064cf8 100644
--- a/src/Login/LoginMiddleware.php
+++ b/src/Login/LoginMiddleware.php
@@ -13,6 +13,10 @@
 use Yiisoft\Auth\Middleware\Authentication;
 use Yiisoft\User\CurrentUser;
 
+use function is_bool;
+use function is_scalar;
+use function sprintf;
+
 /**
  * `LoginMiddleware` automatically logs user in if {@see IdentityInterface} instance presents in a request
  * attribute. It is usually put there by {@see Authentication}.
@@ -47,10 +51,16 @@ public function process(ServerRequestInterface $request, RequestHandlerInterface
         if ($identity instanceof IdentityInterface) {
             $this->currentUser->login($identity);
         } else {
-            $this->logger->debug(sprintf(
-                'Unable to authenticate user by token %s. Identity not found.',
-                is_scalar($identity) ? ('"' . $identity . '"') : ('of type ' . get_debug_type($identity)),
-            ));
+            if (is_scalar($identity)) {
+                $token = is_bool($identity)
+                    ? ($identity ? 'true' : 'false')
+                    : ('"' . $identity . '"');
+            } else {
+                $token = 'of type ' . get_debug_type($identity);
+            }
+            $this->logger->debug(
+                sprintf('Unable to authenticate user by token %s. Identity not found.', $token)
+            );
         }
 
         return $handler->handle($request);
diff --git a/tests/Login/Cookie/CookieLoginMiddlewareTest.php b/tests/Login/Cookie/CookieLoginMiddlewareTest.php
index 3b31f4f..f4aaaea 100644
--- a/tests/Login/Cookie/CookieLoginMiddlewareTest.php
+++ b/tests/Login/Cookie/CookieLoginMiddlewareTest.php
@@ -428,7 +428,7 @@ private function getIdentityRepository(IdentityInterface $identity): IdentityRep
 
     private function getRequestWithAutoLoginCookie(
         string $authKey = CookieLoginIdentity::KEY_CORRECT,
-        int $expires = null
+        ?int $expires = null
     ): ServerRequestInterface {
         return $this->getRequestWithCookies([
             'autoLogin' => json_encode([CookieLoginIdentity::ID, $authKey, $expires ?? time() + 3600], JSON_THROW_ON_ERROR),
diff --git a/tests/Login/LoginMiddlewareTest.php b/tests/Login/LoginMiddlewareTest.php
index 78180b7..2b5b30a 100644
--- a/tests/Login/LoginMiddlewareTest.php
+++ b/tests/Login/LoginMiddlewareTest.php
@@ -5,9 +5,11 @@
 namespace Yiisoft\User\Tests\Login;
 
 use HttpSoft\Message\ServerRequest;
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Server\RequestHandlerInterface;
+use stdClass;
 use Yiisoft\Auth\Middleware\Authentication;
 use Yiisoft\Test\Support\EventDispatcher\SimpleEventDispatcher;
 use Yiisoft\User\CurrentUser;
@@ -82,10 +84,35 @@ public function testIdentityNotFound(): void
         $middleware->process($this->createServerRequest(false), $this->createRequestHandler());
 
         $this->assertInstanceOf(GuestIdentity::class, $this->currentUser->getIdentity());
-        $this->assertNull($this->currentUser
-            ->getIdentity()
-            ->getId());
-        $this->assertSame('Unable to authenticate user by token of type null. Identity not found.', $this->logger->getLastMessage());
+        $this->assertNull($this->currentUser->getIdentity()->getId());
+    }
+
+    public static function dataUnableToAuthenticateUserDebugMessage(): iterable
+    {
+        yield ['true', true];
+        yield ['false', false];
+        yield ['"123"', 123];
+        yield ['"10.4"', 10.4];
+        yield ['"hello"', 'hello'];
+        yield ['of type null', null];
+        yield ['of type stdClass', new stdClass()];
+        yield ['of type array', ['a', 'b']];
+    }
+
+    #[DataProvider('dataUnableToAuthenticateUserDebugMessage')]
+    public function testUnableToAuthenticateUserDebugMessage(string $expectedType, mixed $identity): void
+    {
+        $middleware = new LoginMiddleware($this->currentUser, $this->logger);
+
+        $middleware->process(
+            (new ServerRequest())->withAttribute(Authentication::class, $identity),
+            $this->createRequestHandler()
+        );
+
+        $this->assertSame(
+            'Unable to authenticate user by token ' . $expectedType . '. Identity not found.',
+            $this->logger->getLastMessage()
+        );
     }
 
     private function createServerRequest(bool $withIdentity = true): ServerRequestInterface