<?php

class SkinsMoneySignatureValidator
{
    public function isValid(): bool
    {
        $payload = json_decode(@file_get_contents('php://input'), true);
        if (empty($payload)) {
            return false;
        }

        $data = $this->flattenArray($payload);
        $data[] = 'SERVICE_HASH';

        $signature = hash('sha256', implode('|', $data));

        return hash_equals($signature, $payload['signature']);
    }

    private function flattenArray(array $array): array
    {
        unset($array['signature']);

        $return = [];

        array_walk_recursive($array, function ($a) use (&$return) {
            $return[] = $a;
        });

        return $return;
    }
}

$validator = new SkinsMoneySignatureValidator();
if(!$validator->isValid()) {
  http_response_code(403);
  echo 'INVALID_SIGNATURE';
  die();
}