C# AWS4 Signature Issue

[msbeden]

Hello there, I started writing SP API. I have reached this stage: https://github.com/amzn/selling-partner-api-docs/blob/main/guides/en-US/developer-guide/SellingPartnerApiDeveloperGuide.md#step-4-create-and-sign-your-request

I am working in C#. But I couldn't understand the "Authorization" parameter. How can I calculate the "Signature" value in it?

Can you suggest me the method you used?

I run this but the signature is doing it wrong.

using System;
using System.Web;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Security.Cryptography;
using System.Text;
namespace AWS_Signature
{
    public class Program
    {
        public static string url = "https://sellingpartnerapi-eu.amazon.com/fba/inbound/v0/shipments/shipmentId1/preorder/confirm?MarketplaceId=A33AVAJ2PDY3EV&NeedByDate=2021-10-22";
        public static string accessKey = "AKIA....";
        public static string secretkey = "19U9....";
        public static string awsRegion = "eu-west-1";
        public static string awsServiceName = "execute-api";
        public static string xApiKey = "Atza|IwEBIHObxuNXvc0Nr....";

        public static void Main(string[] args)
        {
            // 0. Prepare request message.
            HttpRequestMessage msg = new HttpRequestMessage(HttpMethod.Get, url);
            msg.Headers.Host = msg.RequestUri.Host;

            // Get and save dates ready for further use.
            DateTimeOffset utcNowSaved = DateTimeOffset.UtcNow;
            string amzLongDate = utcNowSaved.ToString("yyyyMMddTHHmmssZ");
            string amzShortDate = utcNowSaved.ToString("yyyyMMdd");

            // Add to headers. 
            msg.Headers.Add("x-amz-date", amzLongDate);
            msg.Headers.Add("x-api-key", xApiKey); // My API call needs an x-api-key passing also for function security.

            // **************************************************** SIGNING PORTION ****************************************************
            // 1. Create Canonical Request            
            var canonicalRequest = new StringBuilder();
            canonicalRequest.Append(msg.Method + "\n");
            canonicalRequest.Append(string.Join("/", msg.RequestUri.AbsolutePath.Split('/').Select(Uri.EscapeDataString)) + "\n");

            canonicalRequest.Append(GetCanonicalQueryParams(msg) + "\n"); // Query params to do.

            var headersToBeSigned = new List<string>();
            foreach (var header in msg.Headers.OrderBy(a => a.Key.ToLowerInvariant(), StringComparer.OrdinalIgnoreCase))
            {
                canonicalRequest.Append(header.Key.ToLowerInvariant());
                canonicalRequest.Append(":");
                canonicalRequest.Append(string.Join(",", header.Value.Select(s => s.Trim())));
                canonicalRequest.Append("\n");
                headersToBeSigned.Add(header.Key.ToLowerInvariant());
            }
            canonicalRequest.Append("\n");

            var signedHeaders = string.Join(";", headersToBeSigned);
            canonicalRequest.Append(signedHeaders + "\n");
            canonicalRequest.Append("e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"); // Signature for empty body.
            // Hash(msg.Content.ReadAsByteArrayAsync().Result);

            // 2. String to sign.            
            string stringToSign = "AWS4-HMAC-SHA256" + "\n" + amzLongDate + "\n" + amzShortDate + "/" + awsRegion + "/" + awsServiceName + "/aws4_request" + "\n" + Hash(Encoding.UTF8.GetBytes(canonicalRequest.ToString()));

            // 3. Signature with compounded elements.
            var dateKey = HmacSha256(Encoding.UTF8.GetBytes("AWS4" + secretkey), amzShortDate);
            var dateRegionKey = HmacSha256(dateKey, awsRegion);
            var dateRegionServiceKey = HmacSha256(dateRegionKey, awsServiceName);
            var signingKey = HmacSha256(dateRegionServiceKey, "aws4_request");

            var signature = ToHexString(HmacSha256(signingKey, stringToSign.ToString()));

            // **************************************************** END SIGNING PORTION ****************************************************

            // Add the Header to the request.
            var credentialScope = amzShortDate + "/" + awsRegion + "/" + awsServiceName + "/aws4_request";
            msg.Headers.TryAddWithoutValidation("Authorization", "AWS4-HMAC-SHA256 Credential=" + accessKey + "/" + credentialScope + ", SignedHeaders=" + signedHeaders + ", Signature=" + signature);

            // Invoke the request with HttpClient.
            HttpClient client = new HttpClient();
            HttpResponseMessage result = client.SendAsync(msg).Result;
            if (result.IsSuccessStatusCode)
            {
                // Inspect the result and payload returned.
                Console.WriteLine(result.Headers);
                Console.WriteLine(result.Content.ReadAsStringAsync().Result);
                // Wait on user.
                Console.ReadLine();
            }
            else
            {
                Console.WriteLine(result.RequestMessage);
            }
        }
        private static string GetCanonicalQueryParams(HttpRequestMessage request)
        {
            var values = new SortedDictionary<string, string>();

            var querystring = HttpUtility.ParseQueryString(request.RequestUri.Query);
            foreach (var key in querystring.AllKeys)
            {
                if (key == null)//Handles keys without values
                {
                    values.Add(Uri.EscapeDataString(querystring[key]), $"{Uri.EscapeDataString(querystring[key])}=");
                }
                else
                {
                    // Escape to upper case. Required.
                    values.Add(Uri.EscapeDataString(key), $"{Uri.EscapeDataString(key)}={Uri.EscapeDataString(querystring[key])}");
                }
            }
            // Put in order - this is important.
            var queryParams = values.Select(a => a.Value);
            return string.Join("&", queryParams);
        }

        public static string Hash(byte[] bytesToHash)
        {
            return ToHexString(SHA256.Create().ComputeHash(bytesToHash));
        }
        private static string ToHexString(IReadOnlyCollection<byte> array)
        {
            var hex = new StringBuilder(array.Count * 2);
            foreach (var b in array)
            {
                hex.AppendFormat("{0:x2}", b);
            }
            return hex.ToString();
        }

        private static byte[] HmacSha256(byte[] key, string data)
        {
            return new HMACSHA256(key).ComputeHash(Encoding.UTF8.GetBytes(data));
        }
    }
}

[abuzuhri]

Try to Use my library handle most of requirement https://github.com/abuzuhri/Amazon-SP-API-CSharp

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