How to use the firebase/app.auth function in firebase

constructor(firebaseHelper, postId) {
    this.firebaseHelper = firebaseHelper;
    // List of all times running on the page.
    this.timers = [];

    // Firebase SDK.
    this.auth = firebase.auth();

    // Pointers to DOM elements.
    this.postElement = $(Post.createPostHtml(postId));
    MaterialUtils.upgradeTextFields(this.postElement);
    this.toast = $('.mdl-js-snackbar');
    this.theatre = $('.fp-theatre');

    // Adds the element to the main UI if thisis the first time this is called.
    if ($('.fp-image-container', '#page-post').children().length === 0) {
      $('.fp-image-container', '#page-post').append(this.postElement);
    }
  }

checkEULAAgreement() {
    return firebase
      .ref(`/users/${firebase.auth().currentUser.uid}/acceptedEULA`)
      .once("value")
      .then(data => data.val());
  }

useEffect(() => {
    fetchUser(firebase.auth());
    return () => undefined;
  }, []);

concatMap(async () => {
      await firebase.auth().signOut();
      return new SignOutSuccess();
    }),
    catchError(error => of(new SignOutFail(error)))

resetPassword(email: string) {
    const fbAuth = firebase.auth();

    return fbAuth.sendPasswordResetEmail(email)
      .then(() => this.notify.update('Password update email sent', 'info'))
      .catch((error) => this.handleError(error));
  }

public render() {
        const user = firebase.auth().currentUser || {} as any;
        const { event, classes, processingReservation } = this.props;
        return (
            
                }

                title={
                    
                        {event.title}
                    
                }
                subheader={{event.price ? `P${event.price}` : 'Free'}}
            />

private get collection(): firebase.firestore.CollectionReference {
    return firebase
      .firestore()
      .collection("users")
      .doc((firebase.auth().currentUser as firebase.User).uid)
      .collection("projects");
  }
}

render() {
    const { loading, user } = this.props.user;
    if (loading && !user) {
      return (
        
      );
    } else if (user) {
      return (
        
      );
    } else {
      return (
        
      );
    }
  }
}

handleLogout() {
    firebase.auth().signOut().then(() => {
      this.setState({
        user: null,
        faves: [],
      });
    });
  }

export const mine = (ref: firebase.firestore.Query) =>
  ref.where('uid', '==', (firebase.auth().currentUser as firebase.User).uid);