Custom Login Form - External to RH SSO

Hello,

After some research, I gather the recommended way to customize the login form for RH SSO, is through the built-in framework, such as the themes and Authentication SPIs. However, if I had a requirement to externalize the login form to a different website/application altogether for various reasons, is there a way to achieve this?

I'm assuming resource-password/direct grant would not satisfy my ask. Not only is it not recommended to pass credentials through the external application, the browser would not have any SSO session established, since that session is established between the RH SSO Auth Server (via cookies/state returned to client on successful login) and browser.

Can anyone let me know if my above assumptions are correct and whether there is a recommended/correct way to use your own login form/application instead of RH SSO's?

Thanks in advance.

Sherman