Use custom scheme for AuthorizationEndpoint

I'm trying to implement the DATEV OAuth2.0/OpenID Connect into my application but I'm occurring some errors...
They don't use a website for mobile authentication on their side but their own app: https://apps.apple.com/app/id943870921
Its scheme to call a login session on both iOS and Android is as followed: `datevsmartlogin://doLogin/`
So when parsing in this URL for the `authorizationEndpoint` and all other required endpoint from the discoveryURL: https://login.datev.de/openid/.well-known/openid-configuration into my own configuration it looks like this
```
serviceConfiguration: const AuthorizationServiceConfiguration(
authorizationEndpoint: 'datevsmartlogin://doLogin/',
tokenEndpoint: 'https://api.datev.de/token',
endSessionEndpoint: 'https://api.datev.de/endsession',
),
```
But when executing the login flow with the flutter_appauth packages there's an error on both Android and iOS denying the use of non https or http endpoints for the authorizationEndpoint.
I have to use the app to make the Authorization so am I missing something here or is this just a problem of the package?
Thanks

Start by reproducing the login flow with the DATEV discovery configuration and inspect where the Android and iOS flows reject the datevsmartlogin:// authorization endpoint. Compare the platform behavior and determine whether both flows can support this custom scheme; done means the DATEV login flow works on Android and iOS, or the limitation is clearly documented.

Written by the indexing model from the issue text.