certificate overhaul

internal/certificate/sign-cert.go

@@ -0,0 +1,74 @@
+package certificate
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+	"time"
+
+	"crypto/rand"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"math/big"
+)
+
+func SignCert(caCertPem, caPrivKeyPem, csrPem string) (string, error) {
+	caCertData, _ := pem.Decode([]byte(caCertPem))
+	caCert, err := x509.ParseCertificate(caCertData.Bytes)
+	if err != nil {
+		return "", fmt.Errorf("parse cert %v", err)
+	}
+
+	pemKey, _ := pem.Decode([]byte(caPrivKeyPem))
+	if pemKey == nil || pemKey.Type != "RSA PRIVATE KEY" {
+		return "", fmt.Errorf("failed to decode PEM block containing private key")
+	}
+	keyPair, err := x509.ParsePKCS1PrivateKey(pemKey.Bytes)
+	if err != nil {
+		return "", fmt.Errorf("private key %v", err)
+	}
+
+	csrData, _ := pem.Decode([]byte(csrPem))
+	csr, err := x509.ParseCertificateRequest(csrData.Bytes)
+	if err != nil {
+		return "", fmt.Errorf("parse csr %v", err)
+	}
+
+	serial, _ := strconv.ParseInt(time.Now().Format("20060102150405"), 10, 64)
+	certTemplate := x509.Certificate{
+		SerialNumber: big.NewInt(serial + 1),
+		Issuer:       caCert.Issuer,
+		Subject: pkix.Name{
+			Organization:  []string{"Kubernetes Mutating Webserver"},
+			Country:       csr.Subject.Country,
+			Province:      []string{"Cluster Service"},
+			Locality:      []string{"Cluster Local"},
+			StreetAddress: csr.Subject.StreetAddress,
+			PostalCode:    csr.Subject.PostalCode,
+		},
+		NotBefore: time.Now(),
+		NotAfter:  time.Now().AddDate(1, 6, 0),
+		KeyUsage:  x509.KeyUsageDigitalSignature,
+		ExtKeyUsage: []x509.ExtKeyUsage{
+			x509.ExtKeyUsageClientAuth,
+			x509.ExtKeyUsageServerAuth,
+		},
+		DNSNames:           csr.DNSNames,
+		Signature:          csr.Signature,
+		SignatureAlgorithm: csr.SignatureAlgorithm,
+		PublicKey:          csr.PublicKey,
+		PublicKeyAlgorithm: csr.PublicKeyAlgorithm,
+	}
+
+	certBytes, err := x509.CreateCertificate(rand.Reader, &certTemplate, caCert, csr.PublicKey, keyPair)
+	if err != nil {
+		return "", fmt.Errorf("sign %v", err)
+	}
+	c := new(bytes.Buffer)
+	pem.Encode(c, &pem.Block{
+		Type:  "CERTIFICATE",
+		Bytes: certBytes,
+	})
+	return c.String(), nil
+}