Cannot seem to access Keychain/Password managers from browser opened on authorization in React Native App

We have a React Native app that opens a browser window for login via react-native-app-auth. Our stakeholders would like to have the app have access to Keychain and/or PW managers on the device on the login screen both for saving credentials and for filling them. We don't seem to be able to either drive this issue in our code or to find documentation.

## Environment

* **Your Identity Provider**: OIDC
* **Platform that you're experiencing the issue on**: both
* **Are you using Expo?** no

Start by reviewing the react-native-app-auth browser authorization flow and its existing documentation for OIDC on both platforms. Determine whether access to device Keychain or password managers is supported in this flow, and document the supported behavior or the missing requirements. Done means the project has a clear, actionable answer for saving and filling credentials.

Written by the indexing model from the issue text.