func GenerateSelfSignedCert(host, certPath, keyPath string) error {
	priv, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return err
	}
	template := x509.Certificate{
		SerialNumber: big.NewInt(1),
		Subject: pkix.Name{
			CommonName: fmt.Sprintf("%s@%d", host, time.Now().Unix()),
		},
		NotBefore: time.Now(),
		NotAfter:  time.Now().Add(time.Hour * 24 * 365),
		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}
	if ip := net.ParseIP(host); ip != nil {
		template.IPAddresses = append(template.IPAddresses, ip)
	} else {
		template.DNSNames = append(template.DNSNames, host)
	}
	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
	if err != nil {
		return err
	}
	certBuffer := bytes.Buffer{}
	if err := pem.Encode(&certBuffer, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
		return err
	}
	keyBuffer := bytes.Buffer{}
	if err := pem.Encode(&keyBuffer, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)}); err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(certPath), os.FileMode(0755)); err != nil {
		return err
	}
	if err := ioutil.WriteFile(certPath, certBuffer.Bytes(), os.FileMode(0644)); err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(keyPath), os.FileMode(0755)); err != nil {
		return err
	}
	if err := ioutil.WriteFile(keyPath, keyBuffer.Bytes(), os.FileMode(0600)); err != nil {
		return err
	}
	return nil
}
GenerateSelfSignedCert creates a self-signed certificate and key for the given host.
Host may be an IP or a DNS name
The certificate will be created with file mode 0644. The key will be created with file mode 0600.
If the certificate or key files already exist, they will be overwritten.
Any parent directories of the certPath or keyPath will be created as needed with file mode 0755.
package util
import (
	"bytes"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"math/big"
	"net"
	"os"
	"path/filepath"
	"time"
)