title: Firebase authentication with another API
body: <p>I am wondering if it is possible to use just the Firebase authentication system together with your own API and database.</p>
  
  <p>It has some nice features I want to take advantage of, however I do not wish to use their database or storage. </p>
  
  <p>The application I am building is an Angular2 and express application with a MongoDB database. </p>
  
  <p>Any answers will be greatly appreciated!</p>