title: SSO with OpenID
body: <p>I trying to find the way to implement the full blown SSO using the OpenID so that user does not need to enter anything on the new site within the SSO.</p>
  <p>I removed all cookies and started experimenting.</p>
  <ol>
  <li>Logged in on stackoverflow.com</li>
  <li>Looked at Fiddler and seen that stackauth.com is being contacted</li>
  <li>started searching to see what is stackauth.com and ended up stackapps.com</li>
  <li><strong>I was RECOGNIZED and logged in to the stackapps.com !</strong></li>
  </ol>
  <p>To repeat, I deleted all cookies at the start.
  Can someone explain to me SSO that stackoverflow uses because I want to build SSO for sites on different domains? Maybe link if it is already explained somewhere.</p>
  <p>Just checked. I gone to SuperUser.com and was initially not logged but after a moment at the top was it was displayed that I am logged in and to refresh that page.</p>
  <p><a href="https://blog.stackoverflow.com/2010/09/global-network-auto-login/">Global Network Auto-Login</a>
  How does this technically work (if it is not secret :) ) ?</p>
  <p><strong>Update</strong><br />
  It is mentioned that HTML5 local storage is the key.<br />
  But, let's say that I don't have a problem with redirecting all of my users to the some central Auth site. What should I store in the cookie of that site? How will I get user information, do I need to write some API? I would like to stay out of writing my API so I don't have to handle all the security problems. I would rather use something existing like OpenID.</p>