createUserWithEmailAndPasswordAsAdmin(
    email: string,
    displayName: string,
    password: string) {

    /*
    The createUserWithEmailAndPassword() function signs
    the user automaticly in, so we have to create a secondary app to create users,
    because we want to stay signed in as Admin.
    */

    const secondaryApp = firebase.initializeApp(environment.admin, 'admin');

    return secondaryApp.auth()
      .createUserWithEmailAndPassword(email, password)
      .then((credential) => {
        this.setUserData(credential.user, displayName);
        secondaryApp.auth().signOut();
        secondaryApp.delete()
          .then(function () {
            console.log('App deleted successfully');
          })
          .catch(function (error) {
            console.log('Error deleting app:', error);
          });
      });
  }

  private setUserData(user, displayName) {
    let classRef: DocumentReference = null;

    const userRef: AngularFirestoreDocument<any> = this.afs.doc(`users/${user.uid}`);
    const data: User = {
      uid: user.uid,
      email: user.email || null,
      displayName: displayName,
      photoURL: user.photoURL || '..',

    return userRef.set(data);
  }