Convert aspx.cs code into .net core api?

How to convert below code into dotnet core? 

 

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Net;

using System.IO;

using CCA.Util;

using System.Collections.Specialized;

using System.Xml;

namespace GetRSA_Kit

{

public partial class GetRSA : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

try

{

string queryUrl = "https://secure.ccavenue.com/transaction/getRSAKey";

string vParams = "";

foreach (string key in Request.Params.AllKeys){

vParams += key + "=" + Request[key] + "&";

}

// Url Connection

String message = postPaymentRequestToGateway(queryUrl, vParams);

Response.Write(message);

}

catch (Exception exp){

Response.Write("Exception " + exp);

}

}

private string postPaymentRequestToGateway(String queryUrl, String urlParam)

{

String message = "";

try

{

StreamWriter myWriter = null;// it will open a http connection with provided url

WebRequest objRequest = WebRequest.Create(queryUrl);//send data using objxmlhttp object

objRequest.Method = "POST";

//objRequest.ContentLength = TranRequest.Length;

objRequest.ContentType = "application/x-www-form-urlencoded";//to set content type

myWriter = new System.IO.StreamWriter(objRequest.GetRequestStream());

myWriter.Write(urlParam);//send data

myWriter.Close();//closed the myWriter object

// Getting Response

System.Net.HttpWebResponse objResponse = (System.Net.HttpWebResponse)objRequest.GetResponse();//receive the responce from objxmlhttp object

using (System.IO.StreamReader sr = new System.IO.StreamReader(objResponse.GetResponseStream()))

{

message = sr.ReadToEnd();

}

}

catch (Exception exception)

{

Console.Write("Exception occured while connection." + exception);

}

return message;

}

}

}