title: How to best add a comment/rating system to an android app
body: <p>I already published an <strong>android app</strong> where you can see a <strong>list of specific objects</strong> and detailed informations about them. The list changes every day but some of the objects can appear again.
  The application is communicating with a PHP server over HTTP and periodically pulls the list of objects.</p>
  
  <p>I now plan to extend the app to make it possible to <strong>rate</strong> the objects and <strong>add a comment</strong> similar to how it is done in the android market. I'd like to avoid forcing the user to sign up for an account for being able to comment.</p>
  
  <p>I see two problems:</p>
  
  <ul>
  <li>The comment-system could be abused by spammers</li>
  <li>A comment could be added from another system</li>
  </ul>
  
  <p>So my questions are:</p>
  
  <ul>
  <li>How to protect the system from <strong>spam</strong>?</li>
  <li>How to <strong>authenticate</strong> the application with the server?</li>
  <li>How do I limit the <strong>number of comments</strong> to one per user and object?</li>
  <li>What about the androids device id? Is it unique enough to use it as identifier for the user?</li>
  <li>Which other problems do you see?</li>
  </ul>