title: REST response code for invalid data
body: <p>What response code should be passed to client in case of following scenarios?</p>
  
  <ol>
  <li>Invalid data passed while user registration like wrong email format</li>
  <li>User name/ Email is already exists</li>
  </ol>
  
  <p>I chose 403. I also found following that I feel can be used.</p>
  
  <blockquote>
    <p>Wikipedia:</p>
    
    <p>412 Precondition Failed : 
        The server does not meet one of the preconditions that the requester
    put on the request</p>
  </blockquote>
  
  <p>Suggest code if I should use other than 403.</p>