无法获取访问令牌和刷新令牌

Question

All ClientID, ClientSecret & RedirectURI placed in the web.config .

<appSettings>      
    <add key="redirectURI" value="http://localhost:55593/oauthplayground" />
    <add key="clientId" value="uX4YpHHNm****ltekoG" />
    <add key="clientSecret" value="K5cSv3izT1GZ9PXnaWWfRWbTv10*****O3JkYFMlWMF3FhBtjyk0FqJduGJZSAL7B1DngJyxgX3KKNSD0Bqdv" />    
</appSettings>

Now from here I got the authentication code.

static string redirectURI = ConfigurationManager.AppSettings["redirectURI"];
static string clientID = ConfigurationManager.AppSettings["clientID"];
static string clientSecret = ConfigurationManager.AppSettings["clientSecret"];

protected void btnclick_Click(object sender, EventArgs e)
{
    Response.Redirect(String.Format("https://d****o.com/o/authorize/?response_type=code&client_id={0}&redirect_uri={1}", clientID, redirectURI));
}

Then I got my authorization code:

3Q8tvb9d0fj232NZZIAIaItUIqtAd7 

(I store this code in label ie lblcode.Text )

Then for Access_token & Refresh token, I use this code:

protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                if (Request.QueryString.Get("code") != null)
                {     string AccessToken = string.Empty;  
                    lblcode.Text = Request.QueryString["code"].ToString();
                    string RefreshToken = ExchangeAuthorizationCode(lblcode.Text, out AccessToken);

                }
            }
        }

   private string ExchangeAuthorizationCode(string code, out string accessToken)
    {
        accessToken = string.Empty;
        string ClientSecret = clientSecret;
        string ClientId = clientID;
        //get this value by opening your web app in browser.    
        string RedirectUrl = redirectURI;
        var Content = "code=" + code + "&client_id=" + ClientId + "&client_secret=" + ClientSecret + "&redirect_uri=" + RedirectUrl + "&grant_type=authorization_code";
        var request = WebRequest.Create("https://drchrono.com/o/token/");
        request.Method = "POST";
        request.AuthenticationLevel = System.Net.Security.AuthenticationLevel.MutualAuthRequired;

        byte[] byteArray = Encoding.UTF8.GetBytes(Content);
        request.ContentType = "application/x-www-urlencoded";
        request.ContentLength = byteArray.Length;
        //ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;
        //System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
        //ServicePointManager.ServerCertificateValidationCallback = (snder, cert, chain, error) => true;
        using (Stream dataStream = request.GetRequestStream())
        {
            dataStream.Write(byteArray, 0, byteArray.Length);
            dataStream.Close();
        }
        var Response = (HttpWebResponse)request.GetResponse();
        Stream responseDataStream = Response.GetResponseStream();
        StreamReader reader = new StreamReader(responseDataStream);
        string ResponseData = reader.ReadToEnd();
        reader.Close();
        responseDataStream.Close();
        Response.Close();
        if (Response.StatusCode == HttpStatusCode.OK)
        {
            var ReturnedToken = JsonConvert.DeserializeObject<Token>(ResponseData);
            if (ReturnedToken.refresh_token != null)
            {
                accessToken = ReturnedToken.access_token;
                return ReturnedToken.refresh_token;
            }
            else
            {
                return null;
            }
        }
        else
        {
            return string.Empty;
        }
    }  

But I'm getting an error:

The request was aborted: Could not create SSL/TLS secure channel.

Note :

• Using POSTMAN, I get my all data. It means all API are working correctly.
• List item Comment in the Code, i used those but the same problems occurrs.
• I also checked my system with IISCrypto.exe in which i can see all my Server, Client Protocols(SSL 2.0, SSL 3.0, TLS 1.0, TLS 1. 1, TLS 1.2) are enabled.

Answer 1

Put this code above

ServicePointManager.Expect100Continue = true;
System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12; 

the following code.
var request = WebRequest.Create("https://drchrono.com/o/token/");'