feat: Implement RSA key generation and initialization for JWT authentication

backend/cmd/api/main.go

@@ -13,7 +13,8 @@ import (
 	"github.com/gin-gonic/gin"
 	swaggerFiles "github.com/swaggo/files"
 	ginSwagger "github.com/swaggo/gin-swagger"
-	_ "github.com/timetracker/backend/docs" // This line is important for swag to work
+	_ "github.com/timetracker/backend/docs"
+	"github.com/timetracker/backend/internal/api/middleware"
 	"github.com/timetracker/backend/internal/api/routes"
 	"github.com/timetracker/backend/internal/config"
 	"github.com/timetracker/backend/internal/models"
@@ -60,6 +61,11 @@ func main() {
 		log.Fatalf("Error migrating database: %v", err)
 	}
 
+	// Initialize JWT keys
+	if err := middleware.InitJWTKeys(); err != nil {
+		log.Fatalf("Error initializing JWT keys: %v", err)
+	}
+
 	// Create Gin router
 	r := gin.Default()
 

backend/internal/api/middleware/jwt_auth.go

@@ -1,7 +1,14 @@
 package middleware
 
 import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
 	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
 	"time"
 
 	"github.com/gin-gonic/gin"
@@ -12,6 +19,148 @@ import (
 	"github.com/timetracker/backend/internal/models"
 )
 
+var (
+	signKey   *rsa.PrivateKey
+	verifyKey *rsa.PublicKey
+)
+
+// InitJWTKeys initializes the JWT keys
+func InitJWTKeys() error {
+	cfg := config.MustLoadConfig()
+
+	// If a secret is provided, we'll use HMAC-SHA256, so no need for certificates
+	if cfg.JWTConfig.Secret != "" {
+		println("Using HMAC-SHA256 for JWT")
+		return nil
+	}
+
+	// Check if keys exist
+	privKeyPath := filepath.Join(cfg.JWTConfig.KeyDir, cfg.JWTConfig.PrivKeyFile)
+	pubKeyPath := filepath.Join(cfg.JWTConfig.KeyDir, cfg.JWTConfig.PubKeyFile)
+
+	keysExist := fileExists(privKeyPath) && fileExists(pubKeyPath)
+
+	// Generate keys if they don't exist and KeyGenerate is true
+	if !keysExist && cfg.JWTConfig.KeyGenerate {
+		println("Generating RSA keys")
+		if err := generateRSAKeys(cfg.JWTConfig); err != nil {
+			return fmt.Errorf("failed to generate RSA keys: %w", err)
+		}
+	} else if !keysExist {
+		return errors.New("JWT keys not found and key generation is disabled")
+	}
+
+	// Load keys
+	var err error
+	signKey, err = loadPrivateKey(privKeyPath)
+	if err != nil {
+		return fmt.Errorf("failed to load private key: %w", err)
+	}
+
+	verifyKey, err = loadPublicKey(pubKeyPath)
+	if err != nil {
+		return fmt.Errorf("failed to load public key: %w", err)
+	}
+
+	return nil
+}
+
+// fileExists checks if a file exists
+func fileExists(path string) bool {
+	_, err := os.Stat(path)
+	return !os.IsNotExist(err)
+}
+
+// generateRSAKeys generates RSA keys and saves them to disk
+func generateRSAKeys(cfg models.JWTConfig) error {
+	// Create key directory if it doesn't exist
+	if err := os.MkdirAll(cfg.KeyDir, 0700); err != nil {
+		return fmt.Errorf("failed to create key directory: %w", err)
+	}
+
+	// Generate private key
+	privateKey, err := rsa.GenerateKey(rand.Reader, cfg.KeyBits)
+	if err != nil {
+		return fmt.Errorf("failed to generate private key: %w", err)
+	}
+
+	// Save private key
+	privKeyPath := filepath.Join(cfg.KeyDir, cfg.PrivKeyFile)
+	privKeyFile, err := os.OpenFile(privKeyPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return fmt.Errorf("failed to create private key file: %w", err)
+	}
+	defer privKeyFile.Close()
+
+	privKeyPEM := &pem.Block{
+		Type:  "RSA PRIVATE KEY",
+		Bytes: x509.MarshalPKCS1PrivateKey(privateKey),
+	}
+
+	if err := pem.Encode(privKeyFile, privKeyPEM); err != nil {
+		return fmt.Errorf("failed to encode private key: %w", err)
+	}
+
+	// Save public key
+	pubKeyPath := filepath.Join(cfg.KeyDir, cfg.PubKeyFile)
+	pubKeyFile, err := os.OpenFile(pubKeyPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
+	if err != nil {
+		return fmt.Errorf("failed to create public key file: %w", err)
+	}
+	defer pubKeyFile.Close()
+
+	pubKeyPEM := &pem.Block{
+		Type:  "RSA PUBLIC KEY",
+		Bytes: x509.MarshalPKCS1PublicKey(&privateKey.PublicKey),
+	}
+
+	if err := pem.Encode(pubKeyFile, pubKeyPEM); err != nil {
+		return fmt.Errorf("failed to encode public key: %w", err)
+	}
+
+	return nil
+}
+
+// loadPrivateKey loads a private key from a file
+func loadPrivateKey(path string) (*rsa.PrivateKey, error) {
+	keyData, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read private key file: %w", err)
+	}
+
+	block, _ := pem.Decode(keyData)
+	if block == nil {
+		return nil, errors.New("failed to parse PEM block containing the private key")
+	}
+
+	privateKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse private key: %w", err)
+	}
+
+	return privateKey, nil
+}
+
+// loadPublicKey loads a public key from a file
+func loadPublicKey(path string) (*rsa.PublicKey, error) {
+	keyData, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read public key file: %w", err)
+	}
+
+	block, _ := pem.Decode(keyData)
+	if block == nil {
+		return nil, errors.New("failed to parse PEM block containing the public key")
+	}
+
+	publicKey, err := x509.ParsePKCS1PublicKey(block.Bytes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse public key: %w", err)
+	}
+
+	return publicKey, nil
+}
+
 // Claims represents the JWT claims
 type Claims struct {
 	UserID    string `json:"userId"`
@@ -100,12 +249,22 @@ func GenerateToken(user *models.User, c *gin.Context) (string, error) {
 		},
 	}
 
-	// Create the token
-	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
-
 	cfg := config.MustLoadConfig()
-	// Sign the token
-	tokenString, err := token.SignedString([]byte(cfg.JWTConfig.Secret))
+	var token *jwt.Token
+	var tokenString string
+	var err error
+
+	// Choose signing method based on configuration
+	if cfg.JWTConfig.Secret != "" {
+		// Use HMAC-SHA256 if a secret is provided
+		token = jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
+		tokenString, err = token.SignedString([]byte(cfg.JWTConfig.Secret))
+	} else {
+		// Use RSA if no secret is provided
+		token = jwt.NewWithClaims(jwt.SigningMethodRS256, claims)
+		tokenString, err = token.SignedString(signKey)
+	}
+
 	if err != nil {
 		return "", err
 	}
@@ -118,14 +277,26 @@ func GenerateToken(user *models.User, c *gin.Context) (string, error) {
 
 // validateToken validates a JWT token and returns the claims
 func validateToken(tokenString string) (*Claims, error) {
+	cfg := config.MustLoadConfig()
+
 	// Parse the token
 	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (any, error) {
-		// Validate the signing method
-		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
-			return nil, errors.New("unexpected signing method")
+		// Check which signing method was used
+		if _, ok := token.Method.(*jwt.SigningMethodHMAC); ok {
+			// HMAC method was used, validate with secret
+			if cfg.JWTConfig.Secret == "" {
+				return nil, errors.New("HMAC signing method used but no secret configured")
+			}
+			return []byte(cfg.JWTConfig.Secret), nil
+		} else if _, ok := token.Method.(*jwt.SigningMethodRSA); ok {
+			// RSA method was used, validate with public key
+			if verifyKey == nil {
+				return nil, errors.New("RSA signing method used but no public key loaded")
+			}
+			return verifyKey, nil
 		}
-		cfg := config.MustLoadConfig()
-		return []byte(cfg.JWTConfig.Secret), nil
+
+		return nil, errors.New("unexpected signing method")
 	})
 
 	if err != nil {

backend/internal/config/config.go

@@ -48,7 +48,7 @@ func LoadConfig() (*Config, error) {
 
 // loadJWTConfig loads JWT configuration from environment
 func loadJWTConfig(cfg *Config) error {
-	cfg.JWTConfig.Secret = getEnv("JWT_SECRET", "default-secret")
+	cfg.JWTConfig.Secret = getEnv("JWT_SECRET", "")
 	defaultDuration := 24 * time.Hour
 	durationStr := getEnv("JWT_TOKEN_DURATION", defaultDuration.String())
 
@@ -58,7 +58,7 @@ func loadJWTConfig(cfg *Config) error {
 	}
 	cfg.JWTConfig.TokenDuration = duration
 
-	keyGenerateStr := getEnv("JWT_KEY_GENERATE", "false")
+	keyGenerateStr := getEnv("JWT_KEY_GENERATE", "true")
 	keyGenerate, err := strconv.ParseBool(keyGenerateStr)
 	if err != nil {
 		return fmt.Errorf("invalid JWT_KEY_GENERATE: %w", err)
@@ -66,6 +66,15 @@ func loadJWTConfig(cfg *Config) error {
 	cfg.JWTConfig.KeyGenerate = keyGenerate
 
 	cfg.JWTConfig.KeyDir = getEnv("JWT_KEY_DIR", "./keys")
+	cfg.JWTConfig.PrivKeyFile = getEnv("JWT_PRIV_KEY_FILE", "jwt.key")
+	cfg.JWTConfig.PubKeyFile = getEnv("JWT_PUB_KEY_FILE", "jwt.key.pub")
+
+	keyBitsStr := getEnv("JWT_KEY_BITS", "2048")
+	keyBits, err := strconv.Atoi(keyBitsStr)
+	if err != nil {
+		return fmt.Errorf("invalid JWT_KEY_BITS: %w", err)
+	}
+	cfg.JWTConfig.KeyBits = keyBits
 
 	return nil
 }

backend/internal/models/jwt.go

@@ -5,6 +5,9 @@ import "time"
 type JWTConfig struct {
 	Secret        string        `env:"JWT_SECRET" default:""`
 	TokenDuration time.Duration `env:"JWT_TOKEN_DURATION" default:"24h"`
-	KeyGenerate   bool          `env:"JWT_KEY_GENERATE" default:"false"`
+	KeyGenerate   bool          `env:"JWT_KEY_GENERATE" default:"true"`
 	KeyDir        string        `env:"JWT_KEY_DIR" default:"./keys"`
+	PrivKeyFile   string        `env:"JWT_PRIV_KEY_FILE" default:"jwt.key"`
+	PubKeyFile    string        `env:"JWT_PUB_KEY_FILE" default:"jwt.key.pub"`
+	KeyBits       int           `env:"JWT_KEY_BITS" default:"2048"`
 }