Add PEM encoder helper

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/crypto/pem/pem.go

@@ -0,0 +1,68 @@
+// Copyright (c) 2025 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+// Package pem provides utilities for encoding certificates and keys in PEM format
+package pem
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+)
+
+func EncodeCertificate(der []byte) []byte {
+	block := &pem.Block{
+		Type:  "CERTIFICATE",
+		Bytes: der,
+	}
+	return pem.EncodeToMemory(block)
+}
+
+func EncodePrivateKey(key crypto.Signer) ([]byte, error) {
+	var keyDER []byte
+	var keyType string
+
+	switch k := key.(type) {
+	case *ecdsa.PrivateKey:
+		der, err := x509.MarshalECPrivateKey(k)
+		if err != nil {
+			return nil, fmt.Errorf("cannot marshal EC private key: %w", err)
+		}
+		keyDER = der
+		keyType = "EC PRIVATE KEY"
+	case *rsa.PrivateKey:
+		keyDER = x509.MarshalPKCS1PrivateKey(k)
+		keyType = "RSA PRIVATE KEY"
+	case ed25519.PrivateKey:
+		der, err := x509.MarshalPKCS8PrivateKey(k)
+		if err != nil {
+			return nil, fmt.Errorf("cannot marshal ED25519 private key: %w", err)
+		}
+		keyDER = der
+		keyType = "PRIVATE KEY"
+	default:
+		return nil, fmt.Errorf("unsupported key type: %T", key)
+	}
+
+	block := &pem.Block{
+		Type:  keyType,
+		Bytes: keyDER,
+	}
+
+	return pem.EncodeToMemory(block), nil
+}