Ensured custom slugs are case sensitive

module/Core/src/Options/UrlShortenerOptions.php

@@ -0,0 +1,40 @@
+<?php
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\Core\Options;
+
+use Zend\Stdlib\AbstractOptions;
+
+class UrlShortenerOptions extends AbstractOptions
+{
+    public const DEFAULT_CHARS = '123456789bcdfghjkmnpqrstvwxyzBCDFGHJKLMNPQRSTVWXYZ';
+
+    // phpcs:disable
+    protected $__strictMode__ = false;
+    // phpcs:enable
+
+    private $shortcodeChars = self::DEFAULT_CHARS;
+    private $validateUrl = true;
+
+    public function getChars(): string
+    {
+        return $this->shortcodeChars;
+    }
+
+    protected function setShortcodeChars(string $shortcodeChars): self
+    {
+        $this->shortcodeChars = empty($shortcodeChars) ? self::DEFAULT_CHARS : $shortcodeChars;
+        return $this;
+    }
+
+    public function isUrlValidationEnabled(): bool
+    {
+        return $this->validateUrl;
+    }
+
+    protected function setValidateUrl($validateUrl): self
+    {
+        $this->validateUrl = (bool) $validateUrl;
+        return $this;
+    }
+}