How do you secure gRPC communication with mTLS?

Mutual TLS (mTLS) requires both client and server to present and validate certificates, providing bidirectional authentication — each side proves its identity cryptographically. Setup: (1) Certificate Authority — create a CA that signs both server and client certificates (cert-manager in Kubernetes, Vault PKI, or manually with OpenSSL); (2) Server configuration (Go): cert, _ := tls.LoadX509KeyPair("server.crt", "server.key"); caCert, _ := ioutil.ReadFile("ca.crt"); caCertPool.AppendCertsFromPEM(caCert); tlsConfig := &tls.Config{ ClientCAs: caCertPool, ClientAuth: tls.RequireAndVerifyClientCert, Certificates: []tls.Certificate{cert} }; (3) Client configuration: similarly loads client certificate and the CA cert to validate the server; (4) Service mesh alternative — Istio and Linkerd automatically inject Envoy sidecars that handle mTLS transparently, without application code changes, using short-lived certificates rotated automatically. mTLS is the foundation of zero-trust service-to-service security.