What are best practices/methods in preventing ajax requests and or form submisions from pages that my server did not serve?

Knowing that anyone can see my AJAX URL string and or forms how can I prevent calls 开发者_开发知识库or submissions from pages that my server did not serve?

Verifying the source of the form submission is best done by using cookies/sessions. Authenticating each request is your best protection against such cross-site attacks.