An HTTPS server that generates it's own cert in memory.

selfSigningHttpsServer.go

package main

import (
	"bytes"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"log"
	"math/big"
	"net"
	"net/http"
	"os"
	"strings"
	"time"
)

func main() {
	certPem, keyPem, err := generateCert("127.0.0.1", "testing", time.Now(), time.Minute)
	if err != nil {
		panic(err)
	}
	cert, err := tls.X509KeyPair(keyPem, certPem)
	if err != nil {
		panic(err)
	}
	mux := http.NewServeMux()
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintf(w, "Hello, world!")
	})
	server := &http.Server{
		Addr: ":8443",
		TLSConfig: &tls.Config{
			GetCertificate: func(*tls.ClientHelloInfo) (*tls.Certificate, error) {
				return &cert, nil
			},
		},
		Handler: mux,
	}
	server.ListenAndServeTLS("", "")
}
func generateCert(host, organization string, notBefore time.Time, validFor time.Duration) (certPEMBlock, keyPEMBlock []byte, err error) {
	if len(host) == 0 || len(organization) == 0 {
		return certPEMBlock, keyPEMBlock, fmt.Errorf("Missing required --host parameter")
	}
	const rsaBits = 2048
	priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return certPEMBlock, keyPEMBlock, err
	}
	notAfter := notBefore.Add(validFor)
	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		return certPEMBlock, keyPEMBlock, err
	}
	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{organization},
		},
		NotBefore:             notBefore,
		NotAfter:              notAfter,
		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}
	hosts := strings.Split(host, ",")
	for _, h := range hosts {
		if ip := net.ParseIP(h); ip != nil {
			template.IPAddresses = append(template.IPAddresses, ip)
		} else {
			template.DNSNames = append(template.DNSNames, h)
		}
	}
	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, publicKey(priv), priv)
	if err != nil {
		return certPEMBlock, keyPEMBlock, err
	}
	pemBlocks := pemBlockForKey(priv)
	certOutBytes := bytes.NewBuffer(make([]byte, 0, len(derBytes)))
	keyOutBytes := bytes.NewBuffer(make([]byte, 0, len(pemBlocks.Bytes)))
	pem.Encode(certOutBytes, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
	log.Print("written certOutBytes\n")
	// keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	// if err != nil {
	// 	log.Print("failed to open key.pem for writing:", err)
	// 	return
	// }
	pem.Encode(keyOutBytes, pemBlocks)
	// keyOut.Close()
	log.Print("written keyOutBytes\n")
	return keyOutBytes.Bytes(), certOutBytes.Bytes(), nil
}
func publicKey(priv interface{}) interface{} {
	switch k := priv.(type) {
	case *rsa.PrivateKey:
		return &k.PublicKey
	case *ecdsa.PrivateKey:
		return &k.PublicKey
	default:
		return nil
	}
}
func pemBlockForKey(priv interface{}) *pem.Block {
	switch k := priv.(type) {
	case *rsa.PrivateKey:
		return &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(k)}
	case *ecdsa.PrivateKey:
		b, err := x509.MarshalECPrivateKey(k)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Unable to marshal ECDSA private key: %v", err)
			os.Exit(2)
		}
		return &pem.Block{Type: "EC PRIVATE KEY", Bytes: b}
	default:
		return nil
	}
}