<?php 
  function Authlin($authcheckin){
   $app_id = "YOUR_APP_ID";
   $app_secret = "YOUR_APP_SECRET";
   $my_url = "YOUR_URL";

   session_start();
   $code = $authcheckin;

   if(empty($code)) {
     $_SESSION['state'] = md5(uniqid(rand(), TRUE));
     $dialog_url = "http://yourcodeurl.com/dialog/oauth?client_id=" 
       . $app_id . "&redirect_uri=" . urlencode($my_url) . "&state="
       . $_SESSION['state'];

     echo("<script> top.location.href='" . $dialog_url . "'</script>");
   }

   if($_REQUEST['state'] == $_SESSION['state']) {
     $token_url = "https://yourcodeurl.com/oauth/access_token?"
       . "client_id=" . $app_id . "&redirect_uri=" . urlencode($my_url)
       . "&client_secret=" . $app_secret . "&code=" . $code;

     $response = @file_get_contents($token_url);
     $params = null;
     parse_str($response, $params);

     $graph_url = "https://yourcodeurl.com/me?access_token=" 
       . $params['access_token'];

     $user = json_decode(file_get_contents($graph_url));
     echo("Hello " . $user->name);
   }
   else {
     echo("The state does not match.Access Denied.");
   }
}
 ?>

Bind this particular custom function to a button and name that button as generate your link or any anchor does work, better pass it with a JavaScript's through the  action and send the variable or  make a ajax call and send it.....or in the action assign it to the php page and call that function then rest u can read from the below code....formatted....

Generate dynamic link for a specific download authentication......

PHP