Really really simple. Feel free to write your own custom authentication method to fit your project context.
This is download.aspx:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="download.aspx.cs" Inherits="download" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Download Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
</div>
</form>
</body>
</html>
and this is the code behind that file:
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class download : System.Web.UI.Page
{
///
/// Show error to user and close response object.
///
///
private void WriteError(string error) {
Response.Write(error);
Response.End();
}
///
/// Check authentication ticket
///
///
private bool Authenticated() {
//whatever is a session ticket, membership provider base, container in a coded URL querystring parameters, etc..
return true;
}
private string GetRepositoryFolder() {
System.Configuration.AppSettingsReader r = new AppSettingsReader();
return r.GetValue("RepositoryFolder", typeof(string)).ToString();
}
protected void Page_Load(object sender, EventArgs e)
{
if (!Authenticated()){
WriteError("You are not allowed to download this file");
return;
}
else if (Request.QueryString["id"] == null)
{
WriteError("Missing parameter : id");
return;
}
string filePath = System.IO.Path.Combine(GetRepositoryFolder(),Request.QueryString["id"]);
System.IO.FileInfo file = new System.IO.FileInfo(filePath);
if (!file.Exists)
{
WriteError("File doesn't exists");
return;
}
else {
Response.Clear();
Response.AddHeader("Content-Disposition", "attachment; filename=" + file.Name);
Response.AddHeader("Content-Length", file.Length.ToString());
Response.ContentType = "application/octet-stream";
Response.WriteFile(file.FullName);
Response.End();
}
}
}
If successfully authenticated, you will be able to directly download the file:

If not, you will get an error message:
You are not allowed to download this file