title: iOS app crashes when authenticating with Firebase
body: <p>My app blows up when trying to sign in from iPhone simulator. This is a new project and I'm following the <a href="https://firebase.google.com/docs/auth/ios/password-auth" rel="nofollow noreferrer">Firebase docs</a>. When I fill in both input fields and then hit the sign in button, the simulator crashes with <code>Thread 1: breakpoint 1.1</code></p>
  
  <p><strong>LoginVC:</strong></p>
  
  <pre><code>import UIKit
  import Firebase
  import FirebaseAuth
  
  class LoginVC: UIViewController {
  
      override func viewDidLoad() {
          super.viewDidLoad()
      }
  
      @IBOutlet weak var loginEmailInput: UITextField!
      @IBOutlet weak var loginPasswordInput: UITextField!
  
      @IBAction func loginPressed(_ sender: Any) {
          if let email = loginEmailInput.text, let password = loginPasswordInput.text {
  
              FIRAuth.auth()?.signIn(withEmail: email, password: password) { (user, error) in
  
              }
  
          } // breakpoint here
      }
  
  }
  </code></pre>
  
  <p>I've added my app's identifier to the Firebase Console. Installed the correct pods. Added <code>FIRApp.configure()</code> in <code>didFinishLaunchingWithOptions</code>. I'm lost now. Have I missed something?</p>
  
  <p>I've <code>import Firebase</code> in <code>AppDelegate.swift</code>. Do I need to import it in other controllers?</p>