Siteler Arası Talep Sahteciliği (CSRF)

 private const string AntiXsrfTokenKey = "__AntiXsrfToken";
    private const string AntiXsrfUserNameKey = "__AntiXsrfUserName";
    private string _antiXsrfTokenValue;

    protected void Page_Init(object sender, EventArgs e)
    {
        //First, check for the existence of the Anti-XSS cookie
        var requestCookie = Request.Cookies[AntiXsrfTokenKey];
        Guid requestCookieGuidValue;

        //If the CSRF cookie is found, parse the token from the cookie.
        //Then, set the global page variable and view state user
        //key. The global variable will be used to validate that it matches 
        //in the view state form field in the Page.PreLoad method.
        if (requestCookie != null
            && Guid.TryParse(requestCookie.Value, out requestCookieGuidValue))
        {
            //Set the global token variable so the cookie value can be
            //validated against the value in the view state form field in
            //the Page.PreLoad method.
            _antiXsrfTokenValue = requestCookie.Value;

            //Set the view state user key, which will be validated by the
            //framework during each request
            Page.ViewStateUserKey = _antiXsrfTokenValue;
        }
        //If the CSRF cookie is not found, then this is a new session.
        else
        {
            //Generate a new Anti-XSRF token
            _antiXsrfTokenValue = Guid.NewGuid().ToString("N");

            //Set the view state user key, which will be validated by the
            //framework during each request
            Page.ViewStateUserKey = _antiXsrfTokenValue;

            //Create the non-persistent CSRF cookie
            var responseCookie = new HttpCookie(AntiXsrfTokenKey)
            {
                //Set the HttpOnly property to prevent the cookie from
                //being accessed by client side script
                HttpOnly = true,

                //Add the Anti-XSRF token to the cookie value
                Value = _antiXsrfTokenValue
            };

            //If we are using SSL, the cookie should be set to secure to
            //prevent it from being sent over HTTP connections
            if (FormsAuthentication.RequireSSL &&
                Request.IsSecureConnection)
            {
                responseCookie.Secure = true;
            }

            //Add the CSRF cookie to the response
            Response.Cookies.Set(responseCookie);
        }

        Page.PreLoad += master_Page_PreLoad;
    }

    protected void master_Page_PreLoad(object sender, EventArgs e)
    {
        //During the initial page load, add the Anti-XSRF token and user
        //name to the ViewState
        if (!IsPostBack)
        {
            //Set Anti-XSRF token
            ViewState[AntiXsrfTokenKey] = Page.ViewStateUserKey;

            //If a user name is assigned, set the user name
            ViewState[AntiXsrfUserNameKey] =
                   Context.User.Identity.Name ?? String.Empty;
        }
        //During all subsequent post backs to the page, the token value from
        //the cookie should be validated against the token in the view state
        //form field. Additionally user name should be compared to the
        //authenticated users name
        else
        {
            //Validate the Anti-XSRF token
            if ((string)ViewState[AntiXsrfTokenKey] != _antiXsrfTokenValue
                || (string)ViewState[AntiXsrfUserNameKey] !=
                     (Context.User.Identity.Name ?? String.Empty))
            {
                throw new InvalidOperationException("Validation of " +
                                    "Anti-XSRF token failed.");
            }
        }
    }

 if ((context.Request.UrlReferrer == null || context.Request.Url.Host != context.Request.UrlReferrer.Host))
        {
            context.Response.Redirect("~/errorNotFound", false);
            return;
        }