[AngularFire2] Building an Authentication Observable Data Service

export class AuthInfo {
  constructor(private uid$: string){

  }

  isLoggedIn() {
    return !!this.uid$;
  }
}

  static UNKNOW_USER = new AuthInfo(null); // Create a default unknow user
  public authInfo$: BehaviorSubject<AuthInfo> = new BehaviorSubject<AuthInfo>(AuthService.UNKNOW_USER); // We user BehaviorSubject to to conver to Observable, Behavior Subject already needs a default value, so we can repersent logout status by using default value

  login(email, password) {

    return this.fromFirebaseAuthPromise(this.auth$.login({
      email, password
    },{
      method: AuthMethods.Password,
      provider: AuthProviders.Password
    }));
  }

  fromFirebaseAuthPromise(promise) {
    const subject = new Subject<any>();

    promise.then((res) => {
      const uid = this.auth$.getAuth().uid;
      const authInfo = new AuthInfo(uid);
      this.authInfo$.next(authInfo);
      subject.next(res);
      subject.complete();
    }, err => {
      this.authInfo$.error(err);
      subject.error(err);
      subject.complete();
    });

    return subject.asObservable();
  }

      <md-list-item>
        <a
          *ngIf="authInfo$.isLoggedIn()"
          [routerLink]="[‘/heros‘, {outlets: {‘wiki‘: null}}]"
          routerLinkActive="active"
          [routerLinkActiveOptions]="{exact: true}"
        >Heros</a>
      </md-list-item>

  authInfo$;
  constructor(private auth: AuthService){
      this.auth.authInfo$.subscribe(
        res => {
          this.authInfo$ = res;
        }
      )
  }