title: Link Google tokens with FCM Registration tokens
body: <p>I'm currently building a PHP server to send notifications to my users that are registered. They have to log in with Google login method to obtain their tokens and send them to my database. </p>
  
  <p>The problem is that Firebase only send notifications with register tokens. </p>
  
  <p>My question is, how do I link those registered tokens with users google tokens?</p>