<PackageReference Include="Microsoft.Identity.Client" Version="4.89.0" />

Microsoft.Identity.Client.Instance.Discovery.CloudMetadataKeyNames

public static class CloudMetadataKeyNames
Well-known keys for the cloud-specific metadata returned by GetByAuthorityHost.
public const string FederatedCredentialAudience = "federated_credential_audience"

The cloud-specific FIC (Federated Identity Credential) token-exchange audience URI, stored without the /.default suffix (e.g., "api://AzureADTokenExchange"). Use FromAudience to obtain the scope form (with /.default) for client-credentials flows.