Redirect user to requested URL after Login in ASP.Net

I have a requirement that a user can browse site from multiple urls. If user is browsing site directly it will be automatically redirected to login page.

After successful login, I need to redirect user to same url which he requested to browse the site.

I have used below methods but I am not getting null.

P.S - There is no button/link which user is clicking and redirected to login page.

 var url1 = Request.UrlReferrer;
 string referer = Request.Headers["Referer"]