Secure file download from other server
The first thing that pops to mind is to create a custom module, with a menu callback to obfuscate the real url. This is the same way the drupal private filesystem (private://) handles this.


Create a menu entry in your custom module's hook_menu() to obfuscate the real url and perform access checks.

function my_module_menu() {
  $items['my-module/download'] = array(
    'title' =&gt; 'File download',
    'page callback' =&gt; 'my_module_page_callback',
    'access callback' =&gt; TRUE, // Let the page callback handle the checks.
    'type' =&gt; MENU_CALLBACK,
  );
}

Have the page callback transfer the file and check access. Based on file_download().

function my_module_page_callback() {
  $args = func_get_args(); // Get the path elements after `my-module/download`
  $target = implode('/', $args); // Join them into a string.
  $uri = 'http://some-other-server.com/files/' . $target;


  if (function_to_check_if_file_exists($uri)) { // Define this function yourself.
    $headers = array('Content-Type' =&gt; 'file mime-type'); // Set the correct mime-type for the file here.

    if (function_to_check_access()) { // Define this function yourself.
      file_transfer($uri, $headers);
    }
    drupal_access_denied();
  }
  else {
    drupal_not_found();
  }
  drupal_exit();
}



Accessing an url like example.com/my-module/download/documents/1.pdf should now serve a file from http://some-other-server.com/files/documents/1.pdf.

In order to register the files you will have to construct a file object, set the uri to my-module/download/[remote-path] and save the file to the file_managed table. Then attach the file to a node. There might be better ways for this, but this is what I can think of now.

$f = (object) array(
  'uid'         =&gt; 1,
  'filename'    =&gt; '',
  'uri'         =&gt; 'my-module/download/[remote-path]',
  'filemime'    =&gt; '',
  'filesize'    =&gt; 12345,
  'status'      =&gt; 1,
);
file_save($f);

$node = node_load(1);
$node-&gt;field_file[LANGUAGE_NONE][0] = (array)$f; // Add a file field on a content type and use the name here.
node_save($node);