Publish article for Apple news API using C# - (401) Unauthorized

Question

advay_pandya OP

Created Jul ’18

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I am working on posting article using Apple news API.

I created new account and also created new channel.

Below is the code snippet which I am using.

            string channel_id = "{Channel_Id}";
            string api_key_id = "{Key_Id}";
            string api_key_secret = "{Secret}";
            var path = "https://news-api.apple.com/channels/" + channel_id + "/articles";


            var httpWebRequest = (HttpWebRequest)WebRequest.Create(path);
            httpWebRequest.ContentType = "multipart/form-data";
            httpWebRequest.Method = "POST";
            httpWebRequest.Accept = "application/json";
            httpWebRequest.Host = "news-api.apple.com";
            httpWebRequest.UseDefaultCredentials = true;
            httpWebRequest.PreAuthenticate = true;


            httpWebRequest.ProtocolVersion = HttpVersion.Version11;
            httpWebRequest.KeepAlive = true;
            string appleDate = String.Format("{0}Z", DateTime.UtcNow.ToString("s"));
            string credentials = String.Format("{0}:{1}", "Content-Disposition", "form-data; ");
            credentials += String.Format("{0}:{1}", "filename", "article.json; ");
            credentials += String.Format("{0}:{1}", "name", "article.json; ");
       
            credentials += String.Format("{0}","HHMAC; ");
            credentials += String.Format("{0}={1}", "key", api_key_id + "; ");


            string decodedSecret = base64Decode(api_key_secret);
            string canonical_request = path + "POST" + appleDate ;
            string hash = Class1.HmacSha256Digest(canonical_request, decodedSecret);
            string Encodedhash = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(hash));


            credentials += String.Format("{0}={1}", "signature", Encodedhash + "; ");
            credentials += String.Format("{0}={1}", "date", appleDate + "; ");


            httpWebRequest.Headers.Add("Authorization", credentials);


            using (StreamReader r = new StreamReader(Directory.GetCurrentDirectory() + ("/article.json")))
            {
                string json = r.ReadToEnd();
                dynamic jsonObj = JsonConvert.DeserializeObject(json);


                ASCIIEncoding encoding = new ASCIIEncoding();
                Byte[] bytes = encoding.GetBytes(json);
                Stream newStream = httpWebRequest.GetRequestStream();
                newStream.Write(bytes, 0, bytes.Length);
                newStream.Close();
            }
            var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
            using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
            {
                var result = streamReader.ReadToEnd();
            }

Here is base64Decode function

public static string base64Decode(string data)
            {
                var base64EncodedBytes = System.Convert.FromBase64String(data);
                return System.Text.Encoding.UTF8.GetString(base64EncodedBytes);
            }

Here is class to convert Sha256Digest

  public static class Class1
        {
            public static string HmacSha256Digest(this string message, string secret)
            {
                ASCIIEncoding encoding = new ASCIIEncoding();
                byte[] keyBytes = encoding.GetBytes(secret);
                byte[] messageBytes = encoding.GetBytes(message);
                System.Security.Cryptography.HMACSHA256 cryptographer = new System.Security.Cryptography.HMACSHA256(keyBytes);
   
                byte[] bytes = cryptographer.ComputeHash(messageBytes);
   
                return BitConverter.ToString(bytes).Replace("-", "").ToLower();
            }
        }

Whenever I am trying to post the API I am getting below error message:

"'The remote server returned an error: (401) Unauthorized".

When I am trying to post the API request using Postman then I am getting below error message:

  {
        "errors": [
            {
                "code": "WRONG_SIGNATURE"
            }
        ]
    }

Is there anything incorrect to generate Signature ?

I researched few articles but unable to find any solution.

Please guide me to find out the solution on this.

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