How to secure Ajax link requests?

Question

Imagine the next scenario: a user wants to register to a webpage and fills a form. While he is filling the form, jQuery keeps checking through a regular expression if fields

Answer 1

You could use a CSRF token and exit early from your script if you detect that no or an invalid CSRF token. Almost (if not all) PHP frameworks come with support for this.

Also check this question from the security community: https://security.stackexchange.com/questions/23371/csrf-protection-with-custom-headers-and-without-validating-token