Using custom login pages on Flutter.

Hello, we are trying out a POC using Kinde, The SDK flow works fine, we don't want to go down this approach, but rather we want to have our existing login page, to authenticate the users. I found this doc, but it's pretty minimal on how to achieve this on flutter.

https://kinde.com/docs/authentication-and-access/custom-authentication-pages/

Any help would be appreciated.