title: Symfony2 custom user checker based on accepted eula
body: <p>I want to create custom user checker to validate login action against last accepted eula.
  '
  Idea is quite simple, there will be many versions of eula and user <strong>can't</strong> login untill he accept the lastest eula.</p>
  
  <p>Scenario is:</p>
  
  <ol>
  <li>User creates new account and accepts eula.</li>
  <li>Eula gets updated</li>
  <li>User tries to login, but he didnt accept lastest eula</li>
  <li>User gets the same login form but with additional field "accept newest eula" </li>
  <li>User logs in and system inserts information: Current date and time, User id, Eula id to keep track of eula acceptance.</li>
  </ol>
  
  <p>I found this:
  <a href="https://groups.google.com/forum/#!msg/symfony2/D0V0bFks9S0/Qg9mrbpfB3IJ">https://groups.google.com/forum/#!msg/symfony2/D0V0bFks9S0/Qg9mrbpfB3IJ</a></p>
  
  <p>But unfortunately there is no full version of custom user checker. How do I implement the rest of it?</p>