[management, reverse proxy] Add reverse proxy feature (#5291)

* implement reverse proxy


---------

Co-authored-by: Alisdair MacLeod <git@alisdairmacleod.co.uk>
Co-authored-by: mlsmaycon <mlsmaycon@gmail.com>
Co-authored-by: Eduard Gert <kontakt@eduardgert.de>
Co-authored-by: Viktor Liu <viktor@netbird.io>
Co-authored-by: Diego Noguês <diego.sure@gmail.com>
Co-authored-by: Diego Noguês <49420+diegocn@users.noreply.github.com>
Co-authored-by: Bethuel Mmbaga <bethuelmbaga12@gmail.com>
Co-authored-by: Zoltan Papp <zoltan.pmail@gmail.com>
Co-authored-by: Ashley Mensah <ashleyamo982@gmail.com>

management/internals/modules/reverseproxy/sessionkey/sessionkey.go

@@ -0,0 +1,69 @@
+package sessionkey
+
+import (
+	"crypto/ed25519"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+
+	"github.com/netbirdio/netbird/proxy/auth"
+)
+
+type KeyPair struct {
+	PrivateKey string
+	PublicKey  string
+}
+
+type Claims struct {
+	jwt.RegisteredClaims
+	Method auth.Method `json:"method"`
+}
+
+func GenerateKeyPair() (*KeyPair, error) {
+	pub, priv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		return nil, fmt.Errorf("generate ed25519 key: %w", err)
+	}
+
+	return &KeyPair{
+		PrivateKey: base64.StdEncoding.EncodeToString(priv),
+		PublicKey:  base64.StdEncoding.EncodeToString(pub),
+	}, nil
+}
+
+func SignToken(privKeyB64, userID, domain string, method auth.Method, expiration time.Duration) (string, error) {
+	privKeyBytes, err := base64.StdEncoding.DecodeString(privKeyB64)
+	if err != nil {
+		return "", fmt.Errorf("decode private key: %w", err)
+	}
+
+	if len(privKeyBytes) != ed25519.PrivateKeySize {
+		return "", fmt.Errorf("invalid private key size: got %d, want %d", len(privKeyBytes), ed25519.PrivateKeySize)
+	}
+
+	privKey := ed25519.PrivateKey(privKeyBytes)
+
+	now := time.Now()
+	claims := Claims{
+		RegisteredClaims: jwt.RegisteredClaims{
+			Issuer:    auth.SessionJWTIssuer,
+			Subject:   userID,
+			Audience:  jwt.ClaimStrings{domain},
+			ExpiresAt: jwt.NewNumericDate(now.Add(expiration)),
+			IssuedAt:  jwt.NewNumericDate(now),
+			NotBefore: jwt.NewNumericDate(now),
+		},
+		Method: method,
+	}
+
+	token := jwt.NewWithClaims(jwt.SigningMethodEdDSA, claims)
+	signedToken, err := token.SignedString(privKey)
+	if err != nil {
+		return "", fmt.Errorf("sign token: %w", err)
+	}
+
+	return signedToken, nil
+}