Encrypt connector sensitive data

Add database field level encryption level to sensitive data to reduce
the risk in term of data leak. I dedice to have only one key for now in
a near future I may move to one master key and one encryption key per
organization to make rotation easiest.

I don't use built-in pg_crypto function to have clear seperation and
avoid any encryption key leak.

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

pkg/crypto/cipher/cipher.go

@@ -0,0 +1,116 @@
+// 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 cipher
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+)
+
+type (
+	EncryptionKey [32]byte
+)
+
+func NewEncryptionKey(key string) (EncryptionKey, error) {
+	if len(key) != 32 {
+		return EncryptionKey{}, fmt.Errorf("key must be 32 bytes for AES-256")
+	}
+
+	var encryptionKey EncryptionKey
+	copy(encryptionKey[:], key)
+
+	return encryptionKey, nil
+}
+
+func (k EncryptionKey) Bytes() []byte {
+	return k[:]
+}
+
+func (k *EncryptionKey) UnmarshalJSON(data []byte) error {
+	var key string
+	if err := json.Unmarshal(data, &key); err != nil {
+		return err
+	}
+
+	return k.UnmarshalText([]byte(key))
+}
+
+func (k *EncryptionKey) UnmarshalText(text []byte) error {
+	decoded, err := base64.StdEncoding.DecodeString(string(text))
+	if err != nil {
+		return fmt.Errorf("cannot decode base64 key: %w", err)
+	}
+
+	if len(decoded) != 32 {
+		return fmt.Errorf("key must be 32 bytes for AES-256, got %d bytes after base64 decoding", len(decoded))
+	}
+
+	copy(k[:], decoded)
+	return nil
+}
+
+func (k EncryptionKey) MarshalJSON() ([]byte, error) {
+	return json.Marshal(base64.StdEncoding.EncodeToString(k[:]))
+}
+
+func Encrypt(data []byte, key EncryptionKey) ([]byte, error) {
+	block, err := aes.NewCipher(key.Bytes())
+	if err != nil {
+		return nil, err
+	}
+
+	nonce := make([]byte, 12)
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return nil, err
+	}
+
+	aesgcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	ciphertext := aesgcm.Seal(nonce, nonce, data, nil)
+
+	return ciphertext, nil
+}
+
+func Decrypt(data []byte, key EncryptionKey) ([]byte, error) {
+	block, err := aes.NewCipher(key.Bytes())
+	if err != nil {
+		return nil, err
+	}
+
+	aesgcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(data) < 12 {
+		return nil, fmt.Errorf("ciphertext too short")
+	}
+	nonce, ciphertext := data[:12], data[12:]
+
+	plaintext, err := aesgcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return nil, fmt.Errorf("cannot decrypt: %w", err)
+	}
+
+	return plaintext, nil
+}