Restricting forged access to remote PHP page which is usually accessed through AJAX -

i'm building drupal site has little voting system. have php page takes in parameters , updates voting database accordingly. how allow page accessed through ajax on drupal site otherwise restrict access outside users going url prevent forged voting?

ajax == regular http request. cannot distinguish ajax request "normal access". there no way prevent this.

to prevent wrong votes, need build such security voting system. require registration, use sessions , nonces or whatever necessary. trying "block non-ajax requests" not solution.