generate.go

package nanoauth

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"math/big"
	"time"
)

// Generate is a helper function which generates a tls.Certificate for serving
// TLS requests.
func Generate(host string) (*tls.Certificate, error) {
	priv, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return nil, err
	}

	notBefore := time.Now()

	notAfter := notBefore.Add(365 * 24 * 100 * time.Hour) // 100 years..

	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		return nil, err
	}

	template := x509.Certificate{
		DNSNames:     []string{host},
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			CommonName:   host,
			Organization: []string{"Nanobox Acme Co"},
		},
		NotBefore: notBefore,
		NotAfter:  notAfter,

		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
	if err != nil {
		return nil, err
	}

	cert := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
	key := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)})
	c, err := tls.X509KeyPair(cert, key)
	return &c, err
}