how can i create a squarespace like application?

I have made an RESTful web serivce that depends upon another third party api. The web serivce I have created is used by number of other web applications.Those web applications as well as my web service are hosted in the same server(AWS). for eg : one of the application requested http://ift.tt/1emnHy0 where web-app-id is the id of current web application making request to the web serivce. So after making a request to the url, it will get a json response relating to only that particular web-app-id. How can I engineer or architect an application like that? I just want basic insight. I am trying to acomplish this using php