Ory's suite of tools, including Ory Kratos, provides a flexible way to manage user registration and login flows. While the specific functionality to block registration of users from specific domains is not directly mentioned in the provided knowledge sources, you can leverage the concept of hooks and actions in Ory Kratos to achieve this. Hooks in Ory Kratos are configurable and can run before and after a Registration Flow. This can be helpful if you'd like to implement custom logic, such as restricting registration to specific domains. You can use Ory Actions before events such as user registration to enforce certain criteria before the registration flow starts. For example, you can create logic that verifies that the user's email address is associated with a valid domain. Here's a high-level overview of how you might implement this: 1. Configure a hook to run before the registration flow. 2. In this hook, use an Ory Action to check the domain of the user's email address. 3. If the domain is one that you want to block, you can stop the registration flow. Please note that implementing this functionality will require writing custom code that relies on the specifics of your implementation. For more detailed information on how to configure hooks and actions in Ory Kratos, please refer to the [Hook Documentation](https://www.ory.sh/docs/kratos/hooks/configure-hooks) and the [Ory Kratos API Reference](https://www.ory.sh/docs/kratos/reference/api). As for Ory Hydra, it is an OAuth 2.0 and OpenID Connect provider, and it doesn't directly handle user registration. User management, including registration and login, is typically handled by a separate Identity Provider (IdP), which could be Ory Kratos or another system. Therefore, the blocking of registration from specific domains would be handled at the IdP level, not in Hydra.