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Facebook auth provider.

example
// Sign in using a redirect.
firebase.auth().getRedirectResult().then(function(result) {
  if (result.credential) {
    // This gives you a Google Access Token.
    var token = result.credential.accessToken;
  }
  var user = result.user;
})
// Start a sign in process for an unauthenticated user.
var provider = new firebase.auth.FacebookAuthProvider();
provider.addScope('user_birthday');
firebase.auth().signInWithRedirect(provider);
example
// Sign in using a popup.
var provider = new firebase.auth.FacebookAuthProvider();
provider.addScope('user_birthday');
firebase.auth().signInWithPopup(provider).then(function(result) {
  // This gives you a Facebook Access Token.
  var token = result.credential.accessToken;
  // The signed-in user info.
  var user = result.user;
});
see

firebase.auth.Auth.onAuthStateChanged to receive sign in state changes.

Implements