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//-----------------------------------------------------------------------
// <copyright file="Utilities.cs" company="Andrew Arnott">
// Copyright (c) Andrew Arnott. All rights reserved.
// </copyright>
//-----------------------------------------------------------------------
namespace WebFormsRelyingParty.Code {
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Web;
public static class Utilities {
private const string csrfCookieName = "CsrfCookie";
private static readonly RandomNumberGenerator CryptoRandomDataGenerator = new RNGCryptoServiceProvider();
/// <summary>
/// Gets the full URI of the web application root. Guaranteed to end in a slash.
/// </summary>
public static Uri ApplicationRoot {
get {
string appRoot = HttpContext.Current.Request.ApplicationPath;
if (!appRoot.EndsWith("/", StringComparison.Ordinal)) {
appRoot += "/";
}
return new Uri(HttpContext.Current.Request.Url, appRoot);
}
}
public static string SetCsrfCookie() {
// Generate an unpredictable secret that goes to the user agent and must come back
// with authorization to guarantee the user interacted with this page rather than
// being scripted by an evil Consumer.
byte[] randomData = new byte[8];
CryptoRandomDataGenerator.GetBytes(randomData);
string secret = Convert.ToBase64String(randomData);
// Send the secret down as a cookie...
var cookie = new HttpCookie(csrfCookieName, secret) {
Path = HttpContext.Current.Request.Path,
HttpOnly = true,
Expires = DateTime.Now.AddMinutes(30),
};
HttpContext.Current.Response.SetCookie(cookie);
// ...and also return the secret so the caller can save it as a hidden form field.
return secret;
}
public static void VerifyCsrfCookie(string secret) {
var cookie = HttpContext.Current.Request.Cookies[csrfCookieName];
if (cookie != null) {
if (cookie.Value == secret) {
// Valid CSRF check. Clear the cookie and return.
cookie.Expires = DateTime.Now.Subtract(TimeSpan.FromDays(1));
cookie.Value = string.Empty;
if (HttpContext.Current.Request.Browser["supportsEmptyStringInCookieValue"] == "false") {
cookie.Value = "NoCookie";
}
HttpContext.Current.Response.SetCookie(cookie);
return;
}
}
throw new InvalidOperationException("Invalid CSRF check.");
}
}
}
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