title: How to manage multiple accounts login and logout in different browser pages?
body: <p>I have a website built on App Engine(Java) and need user use Google Account to login.</p>
  
  <p>The situation is that:</p>
  
  <ol>
  <li>User Adam has multiple accounts.</li>
  <li>User Adam login with account <em>Adam1</em> and get his <em>Adam1</em> data in browser page A. </li>
  <li>He clicked logout link, but opened it in another tab page B(the same browser of course)</li>
  <li>He login with another account <em>Adam2</em> in browser page B get his <em>Adam2</em> data shown.</li>
  <li>He then returned to browser page A and made some changes to his data and then send to server, at this time my app would recognize the current user is <em>Adam2</em> , and the changes would be taken on <em>Adam2</em>, it does not match the status with its current page A, our user may be confused.</li>
  </ol>
  
  <p>I thought maybe I can attach a userID parameter while making change request to the server and server side will compare the current user id with this userID parameter to make the change request processed or return a refresh command to make the out-of-date page be refreshed to the current account's if the ids are not same.</p>
  
  <p>What is the best practice to handle this situation? </p>