Hi Ahron,
To be completely honest with you, having Windows Integrated Authentication built-in on reactive is not something in our short/mid term roadmap (although we may give ways to do it trough extensibility).
This being said, you can still use a traditional screen that requires it in your reactive authentication flow, login there on preparation (using the username you get from the IntegratedSecurityGetDetails) and redirect back to a reactive screen. As long as you have single sign-on between app types turned on, the user should arrive to the reactive screen already authenticated.
Cheers,
Tiago Simões