title: Single Sign On (SSO) using JWT
body: <p>I have read several articles about sso but could not find an answer in my mind.
  I have a scenario like below:</p>
  
  <p><strong>Scenario:</strong></p>
  
  <ul>
  <li>My company wants to have sso mechanism using jwt.</li>
  <li>Company has 2 different domains like <strong>abc.com</strong> as <strong>abc</strong> and <strong>xyz.com</strong> as <strong>xyz</strong>. </li>
  <li>Also there is a <strong>masterdomain</strong> that manages clients authentication. </li>
  <li>User <strong>X</strong> wants to log in <strong>abc</strong> at first. </li>
  <li><strong>abc</strong> sends credentials to <strong>masterdomain</strong> and <strong>masterdomain</strong> authenticates user then create a signed jwt in order to send back to <strong>abc</strong>.</li>
  <li><strong>abc</strong> keeps this jwt in a cookie. </li>
  <li>After a while if a login to <strong>abc</strong> is attempted at the same computer, system does not ask for credentials and automatically login the user.</li>
  </ul>
  
  <p><strong>Question:</strong></p>
  
  <p>If user tries to open a page in <strong>xyz</strong> domain, how does the system understand that the user loggedin before? I mean <strong>xyz</strong> domain cannot reach the cookie of <strong>abc</strong> which has the jwt. What information should be sent to <strong>xyz</strong> that indicates the user <strong>X</strong> is trying to login? </p>
  
  <p>Thanks in advance</p>