golang mtls server

package main

import (
    "crypto/tls"
    "crypto/x509"
    "io/ioutil"
    "log"
    "net/http"
)

func main() {
    mux := http.NewServeMux()
    mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
        w.Header().Add("Strict-Transport-Security", "max-age=63072000; includeSubDomains")
        w.Write([]byte("Hello mTLS.\n"))
    })

    caCert, _ := ioutil.ReadFile("../step/.step/certs/root_ca.crt")
    caCertPool := x509.NewCertPool()
    caCertPool.AppendCertsFromPEM(caCert)

    tlsConfig := &tls.Config{
        ClientCAs:  caCertPool,
        ClientAuth: tls.RequireAndVerifyClientCert,
    }
    tlsConfig.BuildNameToCertificate()

    server := &http.Server{
        Addr:      ":9443",
        TLSConfig: tlsConfig,
        Handler:   mux,
    }

    log.Fatal(server.ListenAndServeTLS("../cli/server.crt", "../cli/server.key"))
}