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

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

config/secrets/secrets.go

@@ -0,0 +1,121 @@
+package secrets
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+
+	"github.com/micro/go-micro/v3/config"
+)
+
+// NewSecrets returns a config that encrypts values at rest
+func NewSecrets(config config.Config, encryptionKey string) (config.Secrets, error) {
+	return newSecrets(config, encryptionKey)
+}
+
+type secretConf struct {
+	config        config.Config
+	encryptionKey string
+}
+
+func newSecrets(config config.Config, encryptionKey string) (*secretConf, error) {
+	return &secretConf{
+		config:        config,
+		encryptionKey: encryptionKey,
+	}, nil
+}
+
+func (c *secretConf) Get(path string, options ...config.Option) (config.Value, error) {
+	val, err := c.config.Get(path, options...)
+	empty := config.NewJSONValue([]byte("null"))
+	if err != nil {
+		return empty, err
+	}
+	var v interface{}
+	err = json.Unmarshal(val.Bytes(), &v)
+	if err != nil {
+		return empty, err
+	}
+	v, err = convertElements(v, c.fromEncrypted)
+	if err != nil {
+		return empty, err
+	}
+	dat, err := json.Marshal(v)
+	if err != nil {
+		return empty, err
+	}
+	return config.NewJSONValue(dat), nil
+}
+
+func (c *secretConf) Set(path string, val interface{}, options ...config.Option) error {
+	// marshal to JSON and back so we can iterate on the
+	// value without reflection
+	JSON, err := json.Marshal(val)
+	if err != nil {
+		return err
+	}
+	var v interface{}
+	err = json.Unmarshal(JSON, &v)
+	if err != nil {
+		return err
+	}
+	v, err = convertElements(v, c.toEncrypted)
+	if err != nil {
+		return err
+	}
+	return c.config.Set(path, v)
+}
+
+func (c *secretConf) Delete(path string, options ...config.Option) error {
+	return c.config.Delete(path, options...)
+}
+
+func convertElements(elem interface{}, conversionFunc func(elem interface{}) (interface{}, error)) (interface{}, error) {
+	switch m := elem.(type) {
+	case map[string]interface{}:
+		for k, v := range m {
+			conv, err := convertElements(v, conversionFunc)
+			if err != nil {
+				return nil, err
+			}
+			m[k] = conv
+
+		}
+		return m, nil
+	}
+
+	return conversionFunc(elem)
+}
+
+func (c *secretConf) toEncrypted(elem interface{}) (interface{}, error) {
+	dat, err := json.Marshal(elem)
+	if err != nil {
+		return nil, err
+	}
+	encrypted, err := encrypt(string(dat), []byte(c.encryptionKey))
+	if err != nil {
+		return nil, fmt.Errorf("Failed to encrypt: %v", err)
+	}
+	return string(base64.StdEncoding.EncodeToString([]byte(encrypted))), nil
+}
+
+func (c *secretConf) fromEncrypted(elem interface{}) (interface{}, error) {
+	s, ok := elem.(string)
+	if !ok {
+		// This bit decides if the Secrets implementation suppports nonencrypted values
+		// ie. we could do:
+		// return nil, fmt.Errorf("Encrypted values should be strings, but got: %v", elem)
+		// but let's go with not making nonencrypted values blow up the whole thing
+		return elem, nil
+	}
+	dec, err := base64.StdEncoding.DecodeString(s)
+	if err != nil {
+		return elem, nil
+	}
+	decrypted, err := decrypt(string(dec), []byte(c.encryptionKey))
+	if err != nil {
+		return elem, nil
+	}
+	var ret interface{}
+	return ret, json.Unmarshal([]byte(decrypted), &ret)
+}