Develop an Integration plugin for my application

I have a web-applications which conducts online exam. The application is developed in PHP/Mysql. I need to develop a small integration plugin through which other applications can connect to my web-application and can request certain data from my application. The kind of data that will be provided by my application will be simple text strings and urls. (no xml pdf, image or any other kind of data) In short, the process is like this... The client application will send a request through POST to our web-application on a url (lets say... [login to view URL]). Our application will examine the request, do the search on our db and send a response to the client application (on a pre-defined url). The response will have only text, numbers and urls and no other data. I want the developer to develop to write the codes for the client application and the server application to achieve the said objective. A detailed document will be provided to the selected developer before awarding the project and after signing the NDA.