Secret implementation of config. Supporting config merge (#2027)

Co-authored-by: Asim Aslam <asim@aslam.me>

config/secrets/encryption.go

@@ -0,0 +1,70 @@
+package secrets
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+	"io"
+)
+
+// encrypt/decrypt functions are taken from https://www.melvinvivas.com/how-to-encrypt-and-decrypt-data-using-aes/
+
+func encrypt(stringToEncrypt string, key []byte) (string, error) {
+	plaintext := []byte(stringToEncrypt)
+
+	//Create a new Cipher Block from the key
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	//Create a new GCM - https://en.wikipedia.org/wiki/Galois/Counter_Mode
+	//https://golang.org/pkg/crypto/cipher/#NewGCM
+	aesGCM, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	//Create a nonce. Nonce should be from GCM
+	nonce := make([]byte, aesGCM.NonceSize())
+	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
+		return "", err
+	}
+
+	//Encrypt the data using aesGCM.Seal
+	//Since we don't want to save the nonce somewhere else in this case, we add it as a prefix to the encrypted data. The first nonce argument in Seal is the prefix.
+	ciphertext := aesGCM.Seal(nonce, nonce, plaintext, nil)
+	return fmt.Sprintf("%x", ciphertext), nil
+}
+
+func decrypt(encryptedString string, key []byte) (string, error) {
+	enc, _ := hex.DecodeString(encryptedString)
+
+	//Create a new Cipher Block from the key
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	//Create a new GCM
+	aesGCM, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	//Get the nonce size
+	nonceSize := aesGCM.NonceSize()
+
+	//Extract the nonce from the encrypted data
+	nonce, ciphertext := enc[:nonceSize], enc[nonceSize:]
+
+	//Decrypt the data
+	plaintext, err := aesGCM.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return "", err
+	}
+
+	return fmt.Sprintf("%s", plaintext), nil
+}