Add secrets interface to config/secrets (#1325)

* Interface for secrets

* Add secretbox secrets implementation

* Start working on box

* typo

* Add asymmetric encryption implementation

* go mod tidy

* Fix review comments

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

config/secrets/secretbox/secretbox_test.go

@@ -0,0 +1,56 @@
+package secretbox
+
+import (
+	"encoding/base64"
+	"reflect"
+	"testing"
+
+	"github.com/micro/go-micro/v2/config/secrets"
+)
+
+func TestSecretBox(t *testing.T) {
+	secretKey, err := base64.StdEncoding.DecodeString("4jbVgq8FsAV7vy+n8WqEZrl7BUtNqh3fYT5RXzXOPFY=")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	s := NewCodec()
+
+	if err := s.Init(); err == nil {
+		t.Error("Secretbox accepted an empty secret key")
+	}
+	if err := s.Init(secrets.SecretKey([]byte("invalid"))); err == nil {
+		t.Error("Secretbox accepted a secret key that is invalid")
+	}
+
+	if err := s.Init(secrets.SecretKey(secretKey)); err != nil {
+		t.Fatal(err)
+	}
+
+	o := s.Options()
+	if !reflect.DeepEqual(o.SecretKey, secretKey) {
+		t.Error("Init() didn't set secret key correctly")
+	}
+	if s.String() != "nacl-secretbox" {
+		t.Error(s.String() + " should be nacl-secretbox")
+	}
+
+	// Try 10 times to get different nonces
+	for i := 0; i < 10; i++ {
+		message := []byte(`Can you hear me, Major Tom?`)
+
+		encrypted, err := s.Encrypt(message)
+		if err != nil {
+			t.Errorf("Failed to encrypt message (%s)", err)
+		}
+
+		decrypted, err := s.Decrypt(encrypted)
+		if err != nil {
+			t.Errorf("Failed to decrypt encrypted message (%s)", err)
+		}
+
+		if !reflect.DeepEqual(message, decrypted) {
+			t.Errorf("Decrypted Message dod not match encrypted message")
+		}
+	}
+}