### 서명 생성을 구현하는 PHP의 예시: 

```php
<?php
class XsollaWebhookSignature
{
    /**
     * Compute SHA1 signature from webhook JSON body and secret key
     *
     * @param string $jsonBody The raw JSON body from webhook
     * @param string $secretKey The project's secret key
     * @return string The lowercase SHA1 signature
     */
    public static function computeSha1(string $jsonBody, string $secretKey): string
    {
        // Concatenation of the JSON from the request body and the project's secret key
        $dataToSign = $jsonBody . $secretKey;
        // Generate SHA1 signature
        $signature = sha1($dataToSign);
        return strtolower($signature);
    }
    /**
     * Verify webhook signature using timing-safe comparison
     *
     * @param string $jsonBody The raw JSON body from webhook
     * @param string $secretKey The project's secret key  
     * @param string $receivedSignature The signature from authorization header
     * @return bool True if signature is valid, false otherwise
     */
    public static function verifySignature(string $jsonBody, string $secretKey, string $receivedSignature): bool
    {
        $computedSignature = self::computeSha1($jsonBody, $secretKey);
        // Use hash_equals for timing-safe comparison
        return hash_equals($computedSignature, strtolower($receivedSignature));
    }
}
?>
```