getStoredCredentials method
Returns the stored portal credentials, or null if either value is missing.
Implementation
Future<({String username, String password})?> getStoredCredentials() async {
final username = await _secureStorage.read(key: _usernameKey);
final password = await _secureStorage.read(key: _passwordKey);
if (username == null || password == null) return null;
return (username: username, password: password);
}