Unable to launch the registration flow Keycloak / OpenID

I want to force launch the registration flow for ```keycloak``` using `openid` protocols.

I have tried with ```create``` prompt as mentioned in ```OpenID``` [docs](https://openid.net/specs/openid-connect-prompt-create-1_0.html). But, it is not launching the registration flow. Instead, the default auth flow is being launch and User is being asked for login.

### Note:
- Our key cloak setup supports the registration.
- The default auth flow also displays the sign-up label at the bottom of the login button.
- ```'$frontendUrl/realms/$realm/.well-known/openid-configuration'``` also displays the value for ```registration_endpoint```

Following is the code snippet.
```dart
const _appAuth = FlutterAppAuth();
final tokenResponse = await _appAuth.authorizeAndExchangeCode(
AuthorizationTokenRequest(
clientId,
redirectUri,
issuer: '$frontendUrl/realms/$realm',
scopes: ['openid'],
promptValues: ['create'],
allowInsecureConnections: false,
),
);

```

Start with FlutterAppAuth's AuthorizationTokenRequest handling of promptValues and compare the request against the provided Keycloak OpenID configuration. Reproduce the shown issuer and create prompt; done when the registration flow launches instead of the default login flow.

Written by the indexing model from the issue text.