By default, mutual TLS is not enforced. In this section, we will enforce mutual TLS authentication step by step. We will mostly follow the steps in the following link: https://istio.io/docs/tasks/security/authn-policy/#globally-enabling-istio-mutual-tls.
Please read https://istio.io/docs/concepts/security/#authentication-policies and https://istio.io/docs/concepts/security/#mutual-tls-authentication for more details.