title: Multi login using Facebook, Twitter, and internal login issue
body: <p>I am creating an app in which you can login via <a href="http://Facebook" rel="nofollow">Facebook</a>, <a href="http://en.wikipedia.org/wiki/Twitter" rel="nofollow">Twitter</a>, or our own internal mechanism. The issue is the following scenario:</p>
  
  <ol>
  <li>I open the app and login using Facebook</li>
  <li>I logout</li>
  <li>I open the app and login using Twitter</li>
  </ol>
  
  <p>The above scenario will result in me as a user having two accounts in the system. How do I prevent this from happening so that I have one account and it doesn't matter whether I login using Facebook/Twitter?</p>
  
  <p>Every time a user login using Facebook I am as well creating an internal account, with the Facebook username and Facebook id as password. The same thing when I login using Twitter I am creating an internal account with the Twitter user name and id as password.</p>
  
  <p>An idea came in my mind to solve this:</p>
  
  <p>When a user logs in using Twitter check the name and email if a user with that information already exists in the database. However, the name and email they use in both Facebook and Twitter might not be the same, so this might not work all the time.</p>