add tofu cert generation utility

cmd/gencert/main.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"flag"
+	"fmt"
+	"log"
+	"math/big"
+	"os"
+	"strings"
+	"time"
+)
+
+const (
+	keySize    = 4096
+	dateFormat = "2006-01-02"
+)
+
+func main() {
+	keyOut := "key.pem"
+	flag.StringVar(&keyOut, "key", keyOut, "dst file to write private key")
+
+	certOut := "cert.pem"
+	flag.StringVar(&certOut, "cert.pem", certOut, "dst file to write certificate")
+
+	var dnsNames []string
+	flag.Func("dns", "DNS records for cert", func(name string) error {
+		if strings.TrimSpace(name) == "" {
+			return nil
+		}
+		dnsNames = append(dnsNames, name)
+		return nil
+	})
+
+	organization := "dev"
+	flag.StringVar(&organization, "org", organization, "organization which generates the certificate")
+
+	country := "OO"
+	flag.StringVar(&country, "country", country, "country of certificate emitter")
+
+	locality := "ether"
+	flag.StringVar(&locality, "loc", locality, "locality of certificate emitter")
+
+	expiration := time.Now().AddDate(32, 0, 0)
+	flag.Func("exp",
+		"certificate expiration date. Format: "+dateFormat+". Default: "+expiration.Format(dateFormat),
+		func(value string) error {
+			t, errParse := time.Parse(value, dateFormat)
+			if errParse != nil {
+				return errParse
+			}
+			expiration = t
+			return nil
+		})
+	flag.Parse()
+
+	log.Print("generating private key")
+	privKey, errKey := rsa.GenerateKey(rand.Reader, keySize)
+	if errKey != nil {
+		panic(errKey)
+	}
+
+	certTemplate := &x509.Certificate{
+		SerialNumber: big.NewInt(2019),
+		Subject: pkix.Name{
+			Organization: []string{organization},
+			Country:      []string{country},
+			Locality:     []string{locality},
+		},
+		DNSNames:              dnsNames,
+		NotBefore:             time.Now(),
+		NotAfter:              time.Now().AddDate(10, 0, 0),
+		IsCA:                  false,
+		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
+		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
+		BasicConstraintsValid: true,
+	}
+
+	log.Print("generating certificate")
+	certEncoded, errCert := x509.CreateCertificate(rand.Reader, certTemplate, certTemplate, &privKey.PublicKey, privKey)
+	if errCert != nil {
+		panic(errCert)
+	}
+	keyEncoded := x509.MarshalPKCS1PrivateKey(privKey)
+
+	log.Print("writing key and certificate data")
+	if err := writePEM(keyOut, "RSA PRIVATE KEY", keyEncoded); err != nil {
+		panic(err)
+	}
+	if err := writePEM(certOut, "CERTIFICATE", certEncoded); err != nil {
+		panic(err)
+	}
+}
+
+func writePEM(file, name string, data []byte) error {
+	f, errCreate := os.Create(file)
+	if errCreate != nil {
+		return fmt.Errorf("creating file: %w", errCreate)
+	}
+	defer func() { _ = f.Close() }()
+
+	pem.Encode(f, &pem.Block{
+		Type:  name,
+		Bytes: data,
+	})
+	return nil
+}