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gencert.go
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gencert.go
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package virtualbmc
import (
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"fmt"
"math/big"
"os"
"path/filepath"
"strings"
"time"
)
func generateCertificate(host, outDir string, validFor time.Duration) (string, string, error) {
priv, err := rsa.GenerateKey(rand.Reader, 4096)
if err != nil {
return "", "", fmt.Errorf("failed to generate key: %w", err)
}
keyUsage := x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment
notBefore := time.Now()
notAfter := notBefore.Add(validFor)
template := x509.Certificate{
SerialNumber: big.NewInt(1),
Subject: pkix.Name{
CommonName: "placemat",
},
NotBefore: notBefore,
NotAfter: notAfter,
KeyUsage: keyUsage,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
BasicConstraintsValid: true,
DNSNames: dnsAliases(host),
}
certBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, priv.Public(), priv)
if err != nil {
return "", "", fmt.Errorf("failed to create certificate: %w", err)
}
_, err = os.Stat(outDir)
switch {
case err == nil:
case os.IsNotExist(err):
err = os.MkdirAll(outDir, 0755)
if err != nil {
return "", "", fmt.Errorf("failed to create output directory: %w", err)
}
default:
return "", "", fmt.Errorf("stat %s failed: %w", outDir, err)
}
privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
if err != nil {
return "", "", fmt.Errorf("failed to marshal private key: %w", err)
}
cert := filepath.Join(outDir, "cert.pem")
if err := outputPEM(cert, "CERTIFICATE", certBytes); err != nil {
return "", "", err
}
key := filepath.Join(outDir, "key.pem")
if err := outputPEM(key, "PRIVATE KEY", privBytes); err != nil {
return "", "", err
}
return cert, key, nil
}
func dnsAliases(host string) []string {
parts := strings.Split(host, ".")
aliases := make([]string, len(parts))
for i := 0; i < len(parts); i++ {
aliases[i] = strings.Join(parts[0:len(parts)-i], ".")
}
return aliases
}
func outputPEM(fname string, pemType string, data []byte) error {
f, err := os.OpenFile(fname, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
return fmt.Errorf("failed to open %s: %w", fname, err)
}
defer f.Close()
err = pem.Encode(f, &pem.Block{Type: pemType, Bytes: data})
if err != nil {
return fmt.Errorf("failed to encode: %w", err)
}
err = f.Sync()
if err != nil {
return fmt.Errorf("failed to fsync: %w", err)
}
return nil
}