[misc] Separate shared code dependencies (#4288)

* Separate shared code dependencies

* Fix import

* Test respective shared code

* Update openapi ref

* Fix test

* Fix test path

shared/relay/messages/auth/auth.go

@@ -0,0 +1,43 @@
+// Deprecated: This package is deprecated and will be removed in a future release.
+package auth
+
+import (
+	"bytes"
+	"encoding/gob"
+	"fmt"
+)
+
+type Algorithm int
+
+const (
+	AlgoUnknown Algorithm = iota
+	AlgoHMACSHA256
+	AlgoHMACSHA512
+)
+
+func (a Algorithm) String() string {
+	switch a {
+	case AlgoHMACSHA256:
+		return "HMAC-SHA256"
+	case AlgoHMACSHA512:
+		return "HMAC-SHA512"
+	default:
+		return "Unknown"
+	}
+}
+
+type Msg struct {
+	AuthAlgorithm  Algorithm
+	AdditionalData []byte
+}
+
+func UnmarshalMsg(data []byte) (*Msg, error) {
+	var msg *Msg
+
+	buf := bytes.NewBuffer(data)
+	dec := gob.NewDecoder(buf)
+	if err := dec.Decode(&msg); err != nil {
+		return nil, fmt.Errorf("decode Msg: %w", err)
+	}
+	return msg, nil
+}