No, it’s not. You can do it all without the window, there’s a switch for that, or you can just do this:
On the authentication screen just wait. If the dialog is dismissed, add a button to show it again, and go to the next screen with the AuthenticationComplete event. That event only fires when the user has completed the authentication and the fingerprint matched.
I hope you can understand, it’s pretty hard, but I’m not at home so I cannot help you with blocks.