Fix username validation and auto-generation, closes #927

app/Rules/Username.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace Pterodactyl\Rules;
+
+use Illuminate\Contracts\Validation\Rule;
+
+class Username implements Rule
+{
+    public const VALIDATION_REGEX = '/^[a-z0-9]([\w\.-]+)[a-z0-9]$/';
+
+    /**
+     * Validate that a username contains only the allowed characters and starts/ends
+     * with alpha-numeric characters.
+     *
+     * Allowed characters: a-z0-9_-.
+     *
+     * @param string $attribute
+     * @param mixed  $value
+     * @return bool
+     */
+    public function passes($attribute, $value): bool
+    {
+        return preg_match(self::VALIDATION_REGEX, mb_strtolower($value));
+    }
+
+    /**
+     * Return a validation message for use when this rule fails.
+     *
+     * @return string
+     */
+    public function message(): string
+    {
+        return 'The :attribute must start and end with alpha-numeric characters and
+                contain only letters, numbers, dashes, underscores, and periods.';
+    }
+}