Unity/課金/リモートレシート検証/phpサーバ

phpで検証

$receiptJson = '{"orderId":"xxxxxx","productId":"xxxxxx",...}';
$signature = base64_decode('xxxxxxxxxx');

// 下記のURLなどを参考にpem形式に変換
// FYI: http://php.net/manual/ja/ref.openssl.php
$publicKey = der2pem(base64_decode('xxxxxxxxxx'));

if (openssl_verify($receiptJson, $signature, openssl_get_publickey($publicKey)) === 1) {
    // 検証ok
}

参考：https://pakapaka.jp/inapp-google-purchase/