Create a deny-all authorization policy in Istio to restrict access to all services by default. This is necessary to ensure that only authorized traffic is allowed through the service mesh, and to prevent unauthorized access to our applications and services.

By creating a deny-all authorization policy, we can enforce a zero-trust security model and explicitly allow only authorized traffic to access our services.

To implement the deny-all policy, we will need to define a new authorization policy in Istio that denies all requests by default. This policy will apply to all services in the mesh, and we will need to define exceptions for any services that require access.