https_server_cert_lazy.go

package main

import (
	"crypto/tls"
	"fmt"
	"log"
	"net/http"
)

func main() {
	log.SetFlags(log.Lshortfile)

	config := &tls.Config{
		GetCertificate: returnCert,
	}
	ln, err := tls.Listen("tcp", ":443", config)
	if err != nil {
		log.Println(err)
		return
	}
	defer ln.Close()

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintf(w, "Hello TLS!")
	})

	http.Serve(ln, nil)

}

func returnCert(helloInfo *tls.ClientHelloInfo) (*tls.Certificate, error) {
	// helloInfo.ServerName ( This contains our Server Name )
	cer, err := tls.LoadX509KeyPair("server.crt", "server.key")
	if err != nil {
		log.Println(err)
		return nil, nil
	}

	return &cer, nil
}