title: What is the best php login system logic for unique device?
body: <p>I am working on an important project that requires high level security on login authentication.
  The manager of compay told me he wanted to allow clients login just in 1 device (PC, table or mobile phone), so that just that device has access to login in hes account, even when he gives the email and password to someone else, it should not allow others to log in into hes account, so every client has its own account and can be accessed only from one single device.
  I did researches but didn't found very much answers on my question, so what I did till now is this..</p>
  
  <p>After they were registred on database, I added 2 columns on user table named cookie, and the first thing the user saw was "Get access only to your device" page, he pressed button and a cookie was created to hes device and at the same time at the database too, so from there i could make a unique connection for user. Im asking now is there any more secure way to do the unique login for users, like something PC storing file with a key or something else that can not be removed by clearing history data?
  It would be very helpful to give me advices on this section...</p>