title: FOSUserBundle - Symfony2 login with different encoded password
body: <p>I have to do a migration of users from an old database where the passwords are stored in MD5, while in the new application using SHA512.</p>
  
  <p>My purpose is that the old users on first login in the new application must change the password but this implies you can load these users from the database with the password in MD5.</p>
  
  <p>How this can be done using Symfony 2.3.3 + FOSUserBundle?</p>