title: Codeigniter Make Download URL inaccessible in address bar
body: <p>I am creating an application where members as well non members can download books depending upon the category of book available for both users.
  I linked the books to BASE_URL/downloadPDF/11 for prompt download, passing the Id of the book, so that the file location is invisible to user. </p>
  
  <p>Now what I want is no one can get the book downloaded directly pasting the book url(BASE_URL/downloadPDF/11) in browser address bar.
  I tried making function private but It did not work for me.</p>