How to prevent CSRF attack with data not getting saved to DB in ASP.NET with C#?

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C#

ASP.NET

I want to prevent cross site script attack & block data without getting saved to DB. I am generating CSRF Token initially with GUID and then if therein the request cookie we pass that value. Also data can be saved to Database. I am using Visual Studio 2017 and same has been hosted. The check is being done in the Page Init and Page Pre Load Events.

What I have tried:

Below is my code:

#region Code for adding anti-csrf token

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

  protected void Page_Init(object sender, EventArgs e)
  {
      try
      {
          Common.WriteDDSLog("Entered Master Page Init");
          NeSTBLL.Common.ChangeStyle(Page);
          if (!IsPostBack)
          {
              Session["CSRF"] = null;
          }
          else
          {

              if (Request.UrlReferrer == null)
              {
                  //throw new InvalidOperationException("Validation of Anti-XSRF token failed.");
                  Response.Redirect("~/CustomErrorPage.aspx", false);
              }

          }
          // The code below helps to protect against XSRF attacks
          var requestCookie = Request.Cookies[AntiXsrfTokenKey];
          Guid requestCookieGuidValue;
          if (requestCookie != null && Guid.TryParse(requestCookie.Value, out requestCookieGuidValue))
          {
              // Use the Anti-XSRF token from the cookie
              _antiXsrfTokenValue = requestCookie.Value;
              Common.WriteDDSLog("Anti XSRF Token Value 1" + _antiXsrfTokenValue);
              Page.ViewStateUserKey = _antiXsrfTokenValue;
              Common.WriteDDSLog("ViewState User Key 1" + Page.ViewStateUserKey);
          }
          else
          {
              // Generate a new Anti-XSRF token and save to the cookie
              _antiXsrfTokenValue = Guid.NewGuid().ToString("N");
              Common.WriteDDSLog("Anti XSRF Token Value 2" + _antiXsrfTokenValue);
              Page.ViewStateUserKey = _antiXsrfTokenValue;
              Common.WriteDDSLog("ViewState User Key 2" + Page.ViewStateUserKey);
              var responseCookie = new HttpCookie(AntiXsrfTokenKey)
              {
                  HttpOnly = true,
                  Value = _antiXsrfTokenValue
              };
              if (FormsAuthentication.RequireSSL && Request.IsSecureConnection)
              {
                  responseCookie.Secure = true;
              }
              Response.Cookies.Set(responseCookie);
          }

          Page.PreLoad += master_Page_PreLoad;

          //int AbsoluteURL = Request.UrlReferrer.PathAndQuery.ToString().Length;
          //int URL_REF = Request.UrlReferrer.ToString().Length;
          //string URLREF = Request.UrlReferrer.ToString().Substring(0, URL_REF - AbsoluteURL).ToString();

          //Common.WriteDDSLog("Session URLREF : " + Session["URL_REF"].ToString());
          //Common.WriteDDSLog("URLREF1 : " + URLREF);
          //if (Session["URL_REF"].ToString() != URLREF)
          //{
          //    Response.Redirect("~/CustomError.aspx", false);
          //}
      }
      catch (Exception ex)
      {
          FormsAuthentication.SignOut();
          Session.Abandon();
          Session.Clear();
          Response.Clear();
          try
          {
              //Response.Cookies["ASP.NET_SessionId"].Expires = DateTime.Now.AddYears(-30);
              //Response.Cookies.Add(new HttpCookie("ASP.NET_SessionId", ""));
              Response.Cookies.Add(new HttpCookie("ASP.NET_SessionId", ""));
              Response.Cookies["ASP.NET_SessionId"].Expires = DateTime.Now.AddDays(-30); //Delete the cookie
          }
          catch { }


          HttpContext.Current.Response.Redirect("http://", true);
      }
      Common.WriteDDSLog("Completed Master Page Init");
  }

  protected void master_Page_PreLoad(object sender, EventArgs e)
  {
      try
      {

          Common.WriteDDSLog("Entered Master Page Pre Load");
          if (!IsPostBack)
          {
              // Set Anti-XSRF token
              ViewState[AntiXsrfTokenKey] = Page.ViewStateUserKey;
              Common.WriteDDSLog("ViewState Token Key" + ViewState[AntiXsrfTokenKey]);
              ViewState[AntiXsrfUserNameKey] = Context.User.Identity.Name ?? String.Empty;
              Common.WriteDDSLog("ViewState User Name Key" + ViewState[AntiXsrfUserNameKey]);
          }
          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.");
                  Common.WriteDDSLog("Validation of Anti-XSRF token failed in Page Pre Load.");
                  Response.Redirect("~/CustomErrorPage.aspx", false);
              }
          }
      }
      catch (Exception ex)
      {
          FormsAuthentication.SignOut();
          Session.Abandon();
          Session.Clear();
          Response.Clear();
          try
          {
              //Response.Cookies["ASP.NET_SessionId"].Expires = DateTime.Now.AddYears(-30);
              //Response.Cookies.Add(new HttpCookie("ASP.NET_SessionId", ""));
              Response.Cookies.Add(new HttpCookie("ASP.NET_SessionId", ""));
              Response.Cookies["ASP.NET_SessionId"].Expires = DateTime.Now.AddDays(-30); //Delete the cookie
          }
          catch { }

          HttpContext.Current.Response.Redirect("http://", true);
      }
      Common.WriteDDSLog("Completed Master Page Pre Load");
  }