How to securely use reCaptcha with jQuery and PHP

Question

I am writing a user signup form that will use reCaptcha on a jQuery html web page with a PHP backend. When a successful challenge is entered I am not sure how to submit the information to the PHP backend in such a way that it can't be bypassed. The website is running over HTTPS.

I currently check to see if the captcha is correct via using $.ajax() . This submits the recaptcha_challenge_field and recaptcha_response_field to a small PHP script that calls recaptcha_check_answer() and returns success or failure.

Upon success, I can either submit the name, address, phone, etc. fields to another backend PHP script or use another jQuery $.ajax() call.

Either way, a spammer could examine the HTTP requests and submit the form data without using the jQuery front end & reCaptcha.

How can I use reCaptcha and (upon a successful match) submit form data in such a way that a spammer can not easily abuse the system?

Answer 1

I was making this too complicated. I ended up having the ajax call submit the captcha and all of the form data at the same time. If and only if the captcha is correct, then I proceed with the rest of the PHP script. Otherwise, I return an error through the same ajax call.

I added a hidden field via $(#my_input").hide() and check to see if a spammer filled it in. I check the http referrer and sanitize all user input.