[relay] Improve relay messages (#2574)

Co-authored-by: Zoltán Papp <zoltan.pmail@gmail.com>

relay/auth/hmac/v2/validator.go

@@ -0,0 +1,59 @@
+package v2
+
+import (
+	"crypto/hmac"
+	"errors"
+	"fmt"
+	"strconv"
+	"time"
+)
+
+const minLengthUnixTimestamp = 10
+
+type Validator struct {
+	secret []byte
+}
+
+func NewValidator(secret []byte) *Validator {
+	return &Validator{secret: secret}
+}
+
+func (v *Validator) Validate(data any) error {
+	d, ok := data.([]byte)
+	if !ok {
+		return fmt.Errorf("invalid data type")
+	}
+
+	token, err := UnmarshalToken(d)
+	if err != nil {
+		return fmt.Errorf("unmarshal token: %w", err)
+	}
+
+	if len(token.Payload) < minLengthUnixTimestamp {
+		return errors.New("invalid payload: insufficient length")
+	}
+
+	hashFunc := token.AuthAlgo.New()
+	if hashFunc == nil {
+		return fmt.Errorf("unsupported auth algorithm: %s", token.AuthAlgo)
+	}
+
+	h := hmac.New(hashFunc, v.secret)
+	h.Write(token.Payload)
+	expectedMAC := h.Sum(nil)
+
+	if !hmac.Equal(token.Signature, expectedMAC) {
+		return errors.New("invalid signature")
+	}
+
+	timestamp, err := strconv.ParseInt(string(token.Payload), 10, 64)
+	if err != nil {
+		return fmt.Errorf("invalid payload: %w", err)
+	}
+
+	if time.Now().Unix() > timestamp {
+		return fmt.Errorf("expired token")
+	}
+
+	return nil
+}