403 Forbidden error using Webrequest in C# but works in postman

Question

I have an Authorization code which I need to pass in body with some header value when calling an api. When trying the same from postman its working fine but C# Webclient throwing 403 error.

Code below:-

public string GetResponse(string AuthCode) {

string url = "https://example.com//openam/oauth2/access_token?grant_type=authorization_code&realm=/cbpgatqa";
        Uri uri = new Uri(string.Format(url));

        ASCIIEncoding encoding = new ASCIIEncoding();
        string postData = "code=" + AuthCode + "&redirect_uri=" + "http://localhost:8080";
        byte[] data = Encoding.GetEncoding("UTF-8").GetBytes(postData);

        // Create the request
        var httpWebRequest = (HttpWebRequest)WebRequest.Create(uri);
        httpWebRequest.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;
        httpWebRequest.Headers.Add(HttpRequestHeader.Authorization, "Basic " +  "MzE4OGQwYjQtZTRlOC00MTZjLTg5NjAtZDNlYWFhMmNjY2IxOkx3NiVBa0x4NWtPM01rJTJ5RWwxbW1jR0ZYZmhTQmk1NHhIRCpzNiUyVUd5WXN0MCNVbyNMNWQhcVlpZE93djc=");
        httpWebRequest.ContentType = "application/json";
        httpWebRequest.Method = "POST";
        httpWebRequest.ContentLength = data.Length;
        httpWebRequest.UserAgent = @"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.106 Safari/537.36";

        Stream stream = httpWebRequest.GetRequestStream();
        stream.Write(data, 0, data.Length);
        stream.Close();

        // Get the response
        HttpWebResponse httpResponse = null;
        try
        {
            httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
        }
        catch (Exception ex)
        {
            Console.WriteLine("Exception while getting resource " + ex.Message);
            return null;
        }

        string result = null;
        using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
        {
            result = streamReader.ReadToEnd();
        }

        return result;

}

Postman Curl command:-

Generated from a curl request:

curl -X POST ' https://example.com//openam/oauth2/access_token?grant_type=authorization_code&realm=/cbpgatqa ' -H 'Authorization: Basic MzE4OGQwYjQtZTRlOC00MTZjLTg5NjAtZDNlYWFhMmNjY2IxOkx3NiVBa0x4NWtPM01rJTJ5RWwxbW1jR0ZYZmhTQmk1NHhIRCpzNiUyVUd5WXN0MCNVbyNMNWQhcVlpZE93djc=' -H 'Cache-Control: no-cache' -H 'Content-Type: application/x-www-form-urlencoded' -d 'code=93317468-7464-4804-b38a-43e13265c4ac&redirect_uri=http%3A%2F%2Flocalhost%3A8080%2F'

I am not able to figure it out the issue . Can anyone please help me

Answer 1

The Problem solved using RestSharp and passing correct headers value

var client = new RestClient("https://example.com/openam/oauth2/access_token?grant_type=authorization_code&realm=/cbpgatqa");
            var request = new RestRequest(Method.POST);

            request.AddHeader("Content-Type", "application/x-www-form-urlencoded");
            request.AddHeader("Cache-Control", "no-cache");
            request.AddHeader("Authorization", "Basic MzE4OGQwYjQtZTRlOC00MTZjLTg5NjAtZDNlYWFhMmNjY2IxOkx3NiVBa0x4NWtPM01rJTJ5RWwxbW1jR0ZYZmhTQmk1NHhIRCpzNiUyVUd5WXN0MCNVbyNMNWQhcVlpZE93djc=");
            request.AddParameter("undefined", "code=" + AuthCode + "&redirect_uri=http%3A%2F%2Flocalhost%3A8080", ParameterType.RequestBody);
            IRestResponse response = client.Execute(request);

            using (var ms = new MemoryStream(Encoding.Unicode.GetBytes(response.Content)))
            {
                // Deserialization from JSON  
                DataContractJsonSerializer deserializer = new DataContractJsonSerializer(typeof(Token));
                Token token = (Token)deserializer.ReadObject(ms);
            return  userinfo=  GetuserInfo(token.id_token);
            }