auth.ts

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';

import 'rxjs/add/operator/map';
import { Observable } from 'rxjs/Observable';

import * as firebase from 'firebase';

@Injectable()
export class AuthProvider {

  constructor(public http: HttpClient) {
    firebase.auth().onAuthStateChanged((user) => {
      if (user) {
        // User is signed in.
        console.log('User is signed in');
      } else {
        // No user is signed in.
        console.log('User is NOT signed in');      
      }
    });
  }

  /**
   * Use Firebase Web API signInWithEmailAndPassword method
   * to authenticate user login attempt
   * 
   * @method loginWithEmailAndPassword
   * @param email {string}
   * @param password {string}
   * @return {Promise}
   */
  loginWithEmailAndPassword(
    email: string,
    password: string
  ) {
    return new Promise((resolve, reject) => {
      firebase.auth().signInWithEmailAndPassword(email, password).then((val: any) => {
        resolve(val);
      }).catch((error: any) => {
        reject(error);
      });
    });
  }

  /**
   * Log out with Firebase Web API signOutmethod
   * 
   * @method logOut
   * @return {Promise} 
   */
  logOut() {
    return new Promise((resolve, reject) => {
      firebase.auth().signOut().then(() => {
        resolve(true);
      }).catch((error: any) => {
        reject(error);
      });
    });
  }

}