title: Best way to prevent simultaneous login
body: <p>I know this is a recursive question, but, I haven't found a new solution, or a solution based on the new frontend frameworks or technologies.</p>
  
  <p>I've a Vue + PHP application that users can olny log once per time. My current solution to block concurrent access is making a call to a PHP page with Ajax from 5 to 5 minutes storing the time. I store a flag in DB too, whether it has been registered or not. So, when the user try to log in, I check if the time is greater than 6 minutes or the flag is set to 0.</p>
  
  <p>I think this is not the best way to do this. When the application has too many users it can cause too much load on the server.</p>
  
  <p>There is a way to do like Netflix? An warn when triyng to connect and was logged in another machine.</p>