[misc] Move shared components to shared directory (#4286)

Moved the following directories:

```
  - management/client → shared/management/client
  - management/domain → shared/management/domain
  - management/proto → shared/management/proto
  - signal/client → shared/signal/client
  - signal/proto → shared/signal/proto
  - relay/client → shared/relay/client
  - relay/auth → shared/relay/auth
```

and adjusted import paths

shared/relay/auth/hmac/token.go

@@ -0,0 +1,94 @@
+package hmac
+
+import (
+	"bytes"
+	"crypto/hmac"
+	"encoding/base64"
+	"encoding/gob"
+	"fmt"
+	"hash"
+	"strconv"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+)
+
+type Token struct {
+	Payload   string
+	Signature string
+}
+
+func unmarshalToken(payload []byte) (Token, error) {
+	var creds Token
+	buffer := bytes.NewBuffer(payload)
+	decoder := gob.NewDecoder(buffer)
+	err := decoder.Decode(&creds)
+	return creds, err
+}
+
+// TimedHMAC generates a token with TTL and uses a pre-shared secret known to the relay server
+type TimedHMAC struct {
+	secret     string
+	timeToLive time.Duration
+}
+
+// NewTimedHMAC creates a new TimedHMAC instance
+func NewTimedHMAC(secret string, timeToLive time.Duration) *TimedHMAC {
+	return &TimedHMAC{
+		secret:     secret,
+		timeToLive: timeToLive,
+	}
+}
+
+// GenerateToken generates new time-based secret token - basically Payload is a unix timestamp and Signature is a HMAC
+// hash of a timestamp with a preshared TURN secret
+func (m *TimedHMAC) GenerateToken(algo func() hash.Hash) (*Token, error) {
+	timeAuth := time.Now().Add(m.timeToLive).Unix()
+	timeStamp := strconv.FormatInt(timeAuth, 10)
+
+	checksum, err := m.generate(algo, timeStamp)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Token{
+		Payload:   timeStamp,
+		Signature: base64.StdEncoding.EncodeToString(checksum),
+	}, nil
+}
+
+// Validate checks if the token is valid
+func (m *TimedHMAC) Validate(algo func() hash.Hash, token Token) error {
+	expectedMAC, err := m.generate(algo, token.Payload)
+	if err != nil {
+		return err
+	}
+
+	expectedSignature := base64.StdEncoding.EncodeToString(expectedMAC)
+
+	if !hmac.Equal([]byte(expectedSignature), []byte(token.Signature)) {
+		return fmt.Errorf("signature mismatch")
+	}
+
+	timeAuthInt, err := strconv.ParseInt(token.Payload, 10, 64)
+	if err != nil {
+		return fmt.Errorf("invalid payload: %w", err)
+	}
+
+	if time.Now().Unix() > timeAuthInt {
+		return fmt.Errorf("expired token")
+	}
+
+	return nil
+}
+
+func (m *TimedHMAC) generate(algo func() hash.Hash, payload string) ([]byte, error) {
+	mac := hmac.New(algo, []byte(m.secret))
+	_, err := mac.Write([]byte(payload))
+	if err != nil {
+		log.Debugf("failed to generate token: %s", err)
+		return nil, fmt.Errorf("failed to generate token: %w", err)
+	}
+
+	return mac.Sum(nil), nil
+}