Reproducing an error with an absent `RootCAs` parameter

client-server.go

// client/client.go

package main

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

func main() {
	cert, err := ioutil.ReadFile("../rootCA.pem")
	if err != nil {
		log.Fatalf("could not open certificate file: %v", err)
	}

	caCertPool := x509.NewCertPool()
	caCertPool.AppendCertsFromPEM(cert)
	client := http.Client{
		Timeout: time.Minute * 3,
		Transport: &http.Transport{
			TLSClientConfig: &tls.Config{
				RootCAs: caCertPool,
			},
		},
	}
	// change the address to match the common name of the certificate
	resp, err := client.Get("https://localhost:9090")
	if err != nil {
		log.Fatalf("error making get request: %v", err)
	}
	if err != nil {
		log.Fatalf("error making get request: %v", err)
	}

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Fatalf("error reading response: %v", err)
	}
	fmt.Println(string(body))
}

// server/server.go

package main

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

func main() {
	// set up handler to listen to root path
	handler := http.NewServeMux()
	handler.HandleFunc("/", func(writer http.ResponseWriter, request *http.Request) {
		log.Println("new request")
		fmt.Fprintf(writer, "hello world \n")
	})

	// serve on port 9090 of local host
	server := http.Server{
		Addr:    ":9090",
		Handler: handler,
	} // serve the endpoint with tls encryption
	if err := server.ListenAndServeTLS("../webhook.crt", "..//webhook.key"); err != nil {
		log.Fatalf("error listening to port: %v", err)
	}

}