title: How to manage licensing to enable features for a web application?
body: <p>I will be selling a new product that will be managed by a web application on my own servers.
  The web application will allow to manage some devices.</p>
  
  <p>I would like to limit the amount of managable devices to the number of licenses bought by the user.</p>
  
  <p>My web app is currently allowing to manage all the devices with no quantity limitations.</p>
  
  <p>I don't know where to start to implement the licensing (license key generation and checking) nor to limit the devices based on the license keys the user owns.</p>
  
  <p>Any help would be more than welcome.
  Thank you in advance.</p>
  
  <p>FYI: I am using jquery, php and mysql.</p>