HOSN-app/app/src/providers/auth/auth.ts

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Storage } from '@ionic/storage';
import firebase from "firebase";

@Injectable()
export class AuthProvider {
  authProvider: any;

  constructor(public http: HttpClient, private storage: Storage) {
    console.log('Hello AuthProvider Provider');

    var config = {
      apiKey: "AIzaSyCMYjjtPPZak7wBBnh9sy8Yr3Fz1145MuM",
      authDomain: "hybridosn.firebaseapp.com",
      databaseURL: "https://hybridosn.firebaseio.com",
      storageBucket: "hybridosn.appspot.com",
    };
    firebase.initializeApp(config);

    this.authProvider = new firebase.auth.TwitterAuthProvider();
    this.authProvider.setCustomParameters({
      'lang': 'de'
    });
  }

  isLoggedIn() {
    Promise.all([this.storage.get('accessTokenKey'), this.storage.get('accessTokenSecret')])
      .then(values => {
        console.log("looged in: " + (values[0] != null && values[1] != null));
        return values[0] != null && values[1] != null;
      });
  }

  login() {
    return firebase.auth().signInWithPopup(this.authProvider)
      .then(result => {
        this.storage.set('accessTokenKey', result.credential["accessToken"]);
        this.storage.set('accessTokenSecret', result.credential["secret"]);
        return true;
      })
      .catch(error => {
        console.log(error);
        return false;
      })
  }

  logout() {
    this.storage.clear();
  }

}