Develop ready library for API. (PHP/Node.js and JavaScript)

Our JavaScript front-end will request your JavaScript library to sent AJAX request to your back-end, your application is to catch the requests and prevent the abuse as much as possible (spam of requests, illegitimate requests, foreign requests, direct requests etc.). You're to develop JavaScript library/function, which we can use to send AJAX requests to your back-end. We'll pass a string, you make sure it gets to the back-end. Then you're to develop PHP AND Node.js library/function, which will receive sent string and prevent abuse, as well as pass the string to a foreign (our) function (return?). This request in indicative.