title: How to know if a web request is made from particular another known website's link button
body: <p>I have two website </p>
  
  <p>1) Main website: it has a link Help &amp; Training that redirects user to another Help website.</p>
  
  <p>2) Help website has no authentication rules thus anybody can visit the website directly.</p>
  
  <p>Now I have a requirement to allow second website to be visited from first website's link, all the other request should be redirect to another page.</p>
  
  <p>Offcourse querystring/parameter validation is not acceptable as that can be visible and constant</p>
  
  <p>Is it possible, any suggestion is appreciated.</p>