feat: Cert helpers.

pkg/pki/cert.go

@@ -0,0 +1,40 @@
+package pki
+
+import (
+	"crypto/rand"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"math"
+	"math/big"
+	"os"
+)
+
+// Generates a cyrptographically randon number to be used as a cert serial number.
+func NewCertSerialNumber() *big.Int {
+	sn, err := rand.Int(rand.Reader, big.NewInt(math.MaxInt64))
+	if err != nil {
+		panic(errors.New("Could not generate a serial number"))
+	}
+	return sn
+}
+
+// ParseCertFromFile retrieves a certificate stored in PEM format from a file.
+func ParseCertFromFile(fn string) (*x509.Certificate, error) {
+	pemBytes, err := os.ReadFile(fn)
+	if err != nil {
+		return nil, err
+	}
+	certBlock, _ := pem.Decode(pemBytes)
+	if certBlock == nil || certBlock.Type != PEMTypeCertificate {
+		return nil, fmt.Errorf("file was not PEM or first block wasn't %s", PEMTypeCertificate)
+	}
+
+	cert, err := x509.ParseCertificate(certBlock.Bytes)
+	if err != nil {
+		return nil, err
+	}
+
+	return cert, nil
+}