FirebaseUi-Auth mandatory login

I am looking to implement mandatory login, into my website. The problem i am having is that, i cant find a way to do so. Lets say i create a SignIn page like so

  var uiConfig = {
    signInSuccessUrl: '<url-to-redirect-to-on-success>',
    signInOptions: [

      firebase.auth.GoogleAuthProvider.PROVIDER_ID,
      firebase.auth.FacebookAuthProvider.PROVIDER_ID,
      firebase.auth.TwitterAuthProvider.PROVIDER_ID,
      firebase.auth.GithubAuthProvider.PROVIDER_ID,
      firebase.auth.EmailAuthProvider.PROVIDER_ID,
      firebase.auth.PhoneAuthProvider.PROVIDER_ID
    ],

    tosUrl: '<your-tos-url>'
  };


  var ui = new firebaseui.auth.AuthUI(firebase.auth());

  ui.start('#firebaseui-auth-container', uiConfig);
</script>

On a page called www.example.com/SignIn

If i go to www.example.com/Index

I could totally bypass all the signin.

I figured that something like this

 if ( FirebaseUser.getCurrentUser () != null ) {

redirect to sign in page }

How ?

Thanks