<?php
function sign($params, $api_key) {
    $flattened_params = flatten_params($params);
    ksort($flattened_params);
    $base = implode(" ", $flattened_params);

    return hash_hmac("sha256", $base, $api_key);
}

function flatten_params($obj, $result = array(), $path = array()) {
    if (is_array($obj)) {
        foreach ($obj as $k => $v) {
            $result = array_merge($result, flatten_params($v, $result, array_merge($path, array($k))));
        }
    } else {
        $result[implode("", array_map(function($p) { return "[{$p}]"; }, $path))] = $obj;
    }

    return $result;
}

$params = array(
  "version"      => "v10",
  "merchant_id"  => 1,
  "agreement_id" => 1,
  "order_id"     => "0001",
  "amount"       => 100,
  "currency"     => "DKK",
  "continueurl" => "http://shop.domain.tld/continue",
  "cancelurl"   => "http://shop.domain.tld/cancel",
  "callbackurl" => "http://shop.domain.tld/callback",
);

$params["checksum"] = sign($params, "your_secret_payment_window_api_key");
?>

use Digest::SHA qw(hmac_sha256_hex);

sub sign {
    my ($params, $api_key) = @_;
    my $base = join " ", @$params{ sort keys %$params };

    hmac_sha256_hex($base, $api_key);
}

my $params = {
    version      => "v10",
    merchant_id  => 1,
    agreement_id => 1,
    order_id     => "0001",
    amount       => 100,
    currency     => "DKK",
    continueurl => "http://shop.domain.tld/continue",
    cancelurl   => "http://shop.domain.tld/cancel",
    callbackurl => "http://shop.domain.tld/callback"
};

$params->{checksum} = sign($params, "your_secret_payment_window_api_key");

import hmac, hashlib, sys
PY3 = sys.version_info[0] >= 3

def sign(params, api_key):
  items = sorted(params.items(), key=lambda x: x[0])
  base = ' '.join([ str(pair[1]) for pair in items])

  if PY3:
    return hmac.new(
      bytes(api_key, "utf-8"),
      bytes(base, "utf-8"),
      hashlib.sha256
    ).hexdigest()
  else:
    return hmac.new(api_key, base, hashlib.sha256).hexdigest()

params = dict(
 version      = "v10",
 merchant_id  = 1,
 agreement_id = 1,
 order_id     = "0001",
 amount       = 100,
 currency     = "DKK",
 continueurl = "http://shop.domain.tld/continue",
 cancelurl   = "http://shop.domain.tld/cancel",
 callbackurl = "http://shop.domain.tld/callback"
)

params['checksum'] = sign(params, "your_secret_payment_window_api_key")

private string Sign(Dictionary<string, string> params, string api_key) {
    var result = String.Join(" ", params.OrderBy(c => c.Key).Select(c => c.Value).ToArray());
    var e = Encoding.UTF8;
    var hmac = new HMACSHA256(e.GetBytes(api_key));
    byte[] b = hmac.ComputeHash(e.GetBytes(result));
    var s = new StringBuilder();
    for (int i = 0; i < b.Length; i++)
    {
        s.Append(b[i].ToString("x2"));
    }
    return s.ToString();
}

public ActionResult QuickPay() {
    var params = new Dictionary<string, string>();
    params.Add("version", "v10");
    params.Add("merchant_id", "1");
    params.Add("agreement_id", "1");
    params.Add("order_id", "0001");
    params.Add("amount", "100");
    params.Add("currency", "DKK");
    params.Add("continueurl", "http://shop.domain.tld/continue");
    params.Add("cancelurl", "http://shop.domain.tld/cancel");
    params.Add("callbackurl", "http://shop.domain.tld/callback");
    params.Add("language", "da");
    params.Add("autocapture", "1");

    ViewBag.Language = language;
    ViewBag.Autocapture = autocapture;
    ViewBag.OrderId = orderId;
    ViewBag.MerchantId = merchantId;
    ViewBag.AgreementId = agreementId;
    ViewBag.Amount = amount;
    ViewBag.Currency = currency;
    ViewBag.ContinueUrl = continueUrl;
    ViewBag.CancelUrl = cancelUrl;
    ViewBag.CallbackUrl = callbackUrl;
    ViewBag.Checksum = Sign(params, "your_secret_payment_window_api_key");

    return View();
}

const crypto = require('crypto');

function sign(params, api_key) {
  var flattened_params = flatten_params(params);
  var values = Object.keys(flattened_params).sort().map(key => flattened_params[key]).join(' ');
  return crypto.createHmac('sha256', api_key).update(values).digest('hex');
}

function flatten_params(params, result, path) {
  result = result || {};
  path = path || [];
  if (params instanceof Object) {
    var k;
    for (k in params) {
      flatten_params(params[k], result, [...path, k]);
    }
  } else {
    result[path.map(key => '[' + key + ']').join()] = params;
  }
  return result;
}

var params = {
  version: 'v10',
  merchant_id: 1,
  agreement_id: 1,
  amount: 100,
  currency: 'DKK',
  order_id: '0001',
  callbackurl: 'http://shop.domain.tld/callback',
  cancelurl: 'http://shop.domain.tld/cancel',
  continueurl: 'http://shop.domain.tld/continue',
  variables: {
    a: 'b',
    c: 'd'
  }
};

params.checksum = sign(params, 'your_secret_payment_window_api_key');