diff --git a/composer.json b/composer.json
index b68c2b6..eaf9ac5 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^10.0 || ^11.0",
-        "phpstan/phpstan": "^2",
+        "phpstan/phpstan": "^2.1",
         "squizlabs/php_codesniffer": "^3.8",
         "slevomat/coding-standard": "~8.0"
     },
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index e7c9e84..a4942e2 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" backupGlobals="false" bootstrap="vendor/autoload.php" colors="true" processIsolation="false" stopOnFailure="false" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd" cacheDirectory=".phpunit.cache" backupStaticProperties="false">
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" backupGlobals="false" bootstrap="vendor/autoload.php" colors="true" processIsolation="false" stopOnFailure="false" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd" cacheDirectory=".phpunit.cache" backupStaticProperties="false" failOnWarning="true">
     <testsuites>
         <testsuite name="Package Test Suite">
             <directory suffix=".php">./tests/Unit/</directory>
diff --git a/src/Directive.php b/src/Directive.php
index f9874c7..6b71faf 100644
--- a/src/Directive.php
+++ b/src/Directive.php
@@ -25,8 +25,10 @@ public function __construct(protected array $parameters = [])
      */
     public function __toString(): string
     {
-        return implode(', ', array_map(function ($key, $value) {
-            return sprintf('%s="%s"', $key, $value);
-        }, array_keys($this->parameters), $this->parameters));
+        return implode(', ', array_map(
+            fn(mixed $key, mixed $value): string => sprintf('%s="%s"', $key, $value),
+            array_keys($this->parameters),
+            $this->parameters,
+        ));
     }
 }
diff --git a/src/Tokens/HttpAuthentification.php b/src/Tokens/HttpAuthentification.php
index 54736d6..6f445f1 100644
--- a/src/Tokens/HttpAuthentification.php
+++ b/src/Tokens/HttpAuthentification.php
@@ -22,11 +22,11 @@ public function parse(): array
             throw new AuthentificationException('Failed to parse token.');
         }
 
-        if (strtolower(substr($value, 0, 5)) !== 'basic') {
+        if (strtolower(substr((string) $value, 0, 5)) !== 'basic') {
             throw new AuthentificationException('Failed to parse token.');
         }
 
-        $data = explode(':', base64_decode(substr($value, 6)));
+        $data = explode(':', base64_decode(substr((string) $value, 6)));
 
         return [
             'username' => $this->getArrayValue($data, 0),
diff --git a/src/Tokens/HttpAuthorization.php b/src/Tokens/HttpAuthorization.php
index db5595f..04a007d 100644
--- a/src/Tokens/HttpAuthorization.php
+++ b/src/Tokens/HttpAuthorization.php
@@ -22,16 +22,16 @@ public function parse(): array
             throw new AuthentificationException('Failed to parse token.');
         }
 
-        if (strtolower(substr($value, 0, 6)) !== 'digest') {
+        if (strtolower(substr((string) $value, 0, 6)) !== 'digest') {
             throw new AuthentificationException('Failed to parse token.');
         }
 
-        preg_match_all('@(\w+)=(?:(?:")([^"]+)"|([^\s,$]+))@', $value, $matches, PREG_SET_ORDER);
+        preg_match_all('@(\w+)=(?:(?:")([^"]+)"|([^\s,$]+))@', (string) $value, $matches, PREG_SET_ORDER);
 
         $properties = [];
         foreach ($matches as $m) {
             $key = $m[1];
-            $value = $m[2] ? $m[2] : $m[3];
+            $value = $m[2] ?: $m[3];
             $properties[$key] = $value;
         }
 
diff --git a/src/Tokens/PhpAuthDigest.php b/src/Tokens/PhpAuthDigest.php
index 5e55c1c..0164229 100644
--- a/src/Tokens/PhpAuthDigest.php
+++ b/src/Tokens/PhpAuthDigest.php
@@ -22,12 +22,12 @@ public function parse(): array
             throw new AuthentificationException('Failed to parse token.');
         }
 
-        preg_match_all('@(\w+)=(?:(?:")([^"]+)"|([^\s,$]+))@', $value, $matches, PREG_SET_ORDER);
+        preg_match_all('@(\w+)=(?:(?:")([^"]+)"|([^\s,$]+))@', (string) $value, $matches, PREG_SET_ORDER);
 
         $properties = [];
         foreach ($matches as $m) {
             $key = $m[1];
-            $value = $m[2] ? $m[2] : $m[3];
+            $value = $m[2] ?: $m[3];
             $properties[$key] = $value;
         }
 
diff --git a/src/Tokens/RedirectHttpAuthorization.php b/src/Tokens/RedirectHttpAuthorization.php
index df06cb9..6e58080 100644
--- a/src/Tokens/RedirectHttpAuthorization.php
+++ b/src/Tokens/RedirectHttpAuthorization.php
@@ -22,11 +22,11 @@ public function parse(): array
             throw new AuthentificationException('Failed to parse token.');
         }
 
-        if (strtolower(substr($value, 0, 5)) !== 'basic') {
+        if (strtolower(substr((string) $value, 0, 5)) !== 'basic') {
             throw new AuthentificationException('Failed to parse token.');
         }
 
-        list($username, $password) = explode(':', base64_decode(substr($value, 6)));
+        [$username, $password] = explode(':', base64_decode(substr((string) $value, 6)));
 
         return [
             'username' => $username,
diff --git a/src/Vaults/AbstractVault.php b/src/Vaults/AbstractVault.php
index 25a28f1..e858fec 100644
--- a/src/Vaults/AbstractVault.php
+++ b/src/Vaults/AbstractVault.php
@@ -137,11 +137,11 @@ public function setCredentials(string $username, string $password): self
      */
     protected function denyAccess(?string $message = null): void
     {
-        $protocol = isset($_SERVER['SERVER_PROTOCOL']) ? $_SERVER['SERVER_PROTOCOL'] : 'HTTP/1.1';
+        $protocol = $_SERVER['SERVER_PROTOCOL'] ?: 'HTTP/1.1';
         $message = empty($message) ? '<strong>' . $protocol . ' 401 Unauthorized</strong>' : $message;
 
         header($protocol . ' 401 Unauthorized');
-        header('WWW-Authenticate: ' . $this->type()->value . ' ' . (string) $this->directive());
+        header('WWW-Authenticate: ' . $this->type()->value . ' ' . $this->directive());
         exit($message);
     }
 }