import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;

public class HeaderUtil
{
    /*
    Generate the MAC with SHA-256 signature using the necessary keys and HTTP elements
    <param name="merchantId">The provided MID (e.g., "00000000-0000-0000-0000-000000000000") </param>
    <param name="apiKey">The provided API key (e.g., "00000000-0000-0000-0000-000000000000")</param>
    <param name="timestamp">The current Unix Epoch time (in seconds) (e.g., "1634324248" )</param>
    <param name="nonce">Unique Request Identifier (e.g., "00000000-0000-0000-0000-000000000000")</param>
    <param name="uriPath">Path of the request URI (e.g., "items/1")</param>
    <param name="httpVerb">HTTP verb of the request (e.g., "POST")</param>
    <param name="body">Body of the request(e.g., "{ "field1": "value1" }")</param>
    <returns> The signature header for MAC with SHA-256 requests </returns> */

    public String macSignature(String merchantId, String apiKey, String timestamp, String nonce, String uriPath,
                                String httpVerb, String body)
            throws NoSuchAlgorithmException
    {
        String formattedSignature = merchantId + "|" + apiKey + "|" + timestamp
                + "|" + nonce + "|" + uriPath + "|" + httpVerb + "|" + body;
        //remove all whitespace and convert to uppercase
        formattedSignature = formattedSignature.replaceAll("[\\r\\n\\t\\s]", "").toUpperCase();
        //base 64 encode
        String base64EncodedString = Base64.getEncoder().encodeToString(formattedSignature.getBytes());
      
      	MessageDigest digest = null;
        try {
            digest = MessageDigest.getInstance("SHA-256");
        } catch(NoSuchAlgorithmException e) {
            System.out.println("Could not find algorithm");
        }
      
        byte[] sha256Hash = digest.digest(base64EncodedString.getBytes(StandardCharsets.UTF_8));
        return convertBytesToHex(sha256Hash);

    }

    private static String convertBytesToHex(byte[] hash)
    {
        StringBuilder hexString = new StringBuilder(2 * hash.length);
        for (byte b : hash)
        {
            String hex = Integer.toHexString(0xff & b);
            if (hex.length() == 1)
            {
                hexString.append('0');
            }
            hexString.append(hex);
        }
        return hexString.toString();
    }
}

using System;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;

namespace MAC {
    public class HeaderUtility {

        /// <summary>
        /// Generate the MAC signature with SHA-256 using the necessary keys and HTTP elements
        /// </summary>
        /// <param name="merchantId">The provided MID (e.g., "00000000-0000-0000-0000-000000000000") </param>
        /// <param name="apiKey">The provided API key (e.g., "00000000-0000-0000-0000-000000000000")</param>
        /// <param name="timestamp">The current Unix Epoch time (in seconds) (e.g., "1634324248" )</param>
        /// <param name="nonce">Unique Request Identifier (e.g., "00000000-0000-0000-0000-000000000000")</param>
        /// <param name="uriPath">Path of the request URI (e.g., "items/1")</param>
        /// <param name="httpVerb">HTTP verb of the request (e.g., "POST")</param>
        /// <param name="body">Body of the request(e.g., "{ "field1": "value1" }")</param>
        /// <returns>The signature header for MAC with SHA-256 requests </returns>
        public static string GenerateSignature(string merchantId, string apiKey, string timestamp, string nonce, string uriPath, string httpVerb, string body) {
            // Compose signature elements
            string signatureRaw = $"{merchantId}|{apiKey}|{timestamp}|{nonce}|{uriPath}|{httpVerb}|{body}";

            // Remove characters CR, LF, TAB, and whitespace
            string signatureCleaned = Regex.Replace(signatureRaw, @"[\r\n\t\s]", string.Empty);

            // Convert string to upper-case
            string signatureUpper = signatureCleaned.ToUpperInvariant();

            // Base64 encode string
            string signatureBase64 = Convert.ToBase64String(Encoding.UTF8.GetBytes(signatureUpper));

            // SHA-256 hashed string
            using SHA256 sha256 = SHA256.Create();
            byte[] signatureHashedBytes = sha256.ComputeHash(Encoding.UTF8.GetBytes(signatureBase64));
            string signature = string.Join(null, signatureHashedBytes.Select(b => b.ToString("x2")));

            return signature;
        }
    }
}

<?PHP
/**
 * Generate the MAC with SHA-256 signature using the necessary keys and HTTP elements
 * @param string $merchant_id The provided MID (e.g., "00000000-0000-0000-0000-000000000000")
 * @param string $api_key The provided API key (e.g., "00000000-0000-0000-0000-000000000000")
 * @param integer $timestamp The current Unix Epoch time (in seconds) (e.g., "1634324248"
 * @param string $nonce Unique Request Identifier (e.g., "00000000-0000-0000-0000-000000000000")
 * @param string $uri_path Path of the request URI (e.g., "items/1")
 * @param string $http_verb HTTP verb of the request (e.g., "POST")
 * @param string $body Body of the request(e.g., "{ "field1": "value1" }")
 * @return string The signature header for MAC with SHA-256 requests
 */
function mac_signature($merchant_id, $api_key, $timestamp, $nonce, $uri_path, $http_verb, $body)
{
    // Compose signature elements
    $signature_raw = "{$merchant_id}|{$api_key}|{$timestamp}|{$nonce}|{$uri_path}|{$http_verb}|{$body}";

    // Remove characters CR, LF, TAB, and whitespace
    $signature_cleaned = str_replace(array("\r", "\n", "\t", " ") , '', $signature_raw);

    // Convert string to upper-case
    $signature_upper = strtoupper($signature_cleaned);

    // Base64 encode string
    $signature_base64 = base64_encode($signature_upper);

    // SHA-256 encode string
    $signature = hash('sha256', $signature_base64);

    return $signature;
}
?>