RxSwift Login with Firebase

login.swift

logInButton.rx_tap
            .flatMap { [unowned self] () -> Observable<FAuthData> in
                firebaseRef.rx_authUser(self.emailTextField.text!, password: self.passwordTextField.text!)
            }
            .catchError({ (error) -> Observable<String?> in
              return Observable.just(error.someErrorMessage) // figure out what you want to say.
            })
            .observeOn(MainScheduler.instance) //not needed since Firebase will always by default deliver on the MainThread. 
            .subscribeNext { [unowned self] (errorMessage: String?) in
                if let errorMessage = errorMessage else { // SHOW ALERT }
                else { // WE ARE GOOD, self.navigationController?.push }
            }
            .addDisposableTo(disposeBag)