title: How to access Google Play Android Developer API through backend server
body: <p>I am implemented In App Billing for android.I wanted to implement subscription validity checking through my backend server. As Google Play Documentation, for making call for Google Play API,need authentication using oauth 2.0.</p>
  
  <p>I followed instructions for registering project and creating credentials. But from there I have no idea how to use those credentials, I tried authentication via CURL request, but it asking permission as shown in follwing image<img src="https://i.stack.imgur.com/GVyup.png" alt="enter image description here"></p>
  
  <p>This permissions works fine I can exchange code and get access token, but all this done by manually, how should I implement this on backend.
  I even try to use google api php library provided by Google, but It adds confusion. Also they didn't provide any example, how to use library.</p>
  
  <p>Can anybody elaborate how exactly use library or pure php?
  Thanks in advance.</p>