Load or generate signing key from file

server/internal/secrets/jwt_key.go

@@ -0,0 +1,82 @@
+package secrets
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+const (
+	// JWTKeyBytes is the size of the JWT signing key in bytes (256 bits)
+	JWTKeyBytes = 32
+	// JWTKeyFile is the filename for the JWT signing key
+	JWTKeyFile = "jwt_signing_key"
+	// JWTKeyPerm is the file permission for the JWT signing key (owner read/write only)
+	JWTKeyPerm = 0600
+)
+
+// EnsureJWTSigningKey ensures a JWT signing key exists in the secrets directory.
+// If no key exists, it generates and stores a new one with restrictive permissions.
+// Returns the base64-encoded signing key.
+func EnsureJWTSigningKey(secretsDir string) (string, error) {
+	log := getLogger()
+
+	// Ensure the secrets directory exists with restrictive permissions
+	if err := os.MkdirAll(secretsDir, 0700); err != nil {
+		return "", fmt.Errorf("failed to create secrets directory: %w", err)
+	}
+
+	keyPath := filepath.Join(secretsDir, JWTKeyFile)
+
+	// Check if the key file already exists
+	if _, err := os.Stat(keyPath); err == nil {
+		// Key file exists, read it
+		keyBytes, err := os.ReadFile(keyPath)
+		if err != nil {
+			return "", fmt.Errorf("failed to read JWT signing key: %w", err)
+		}
+
+		key := string(keyBytes)
+		if key == "" {
+			return "", fmt.Errorf("JWT signing key file is empty")
+		}
+
+		log.Debug("loaded existing JWT signing key from file")
+		return key, nil
+	}
+
+	// Key file doesn't exist, generate a new key
+	log.Info("generating new JWT signing key")
+	key, err := generateJWTSigningKey()
+	if err != nil {
+		return "", fmt.Errorf("failed to generate JWT signing key: %w", err)
+	}
+
+	// Write the key to the file with restrictive permissions
+	if err := os.WriteFile(keyPath, []byte(key), JWTKeyPerm); err != nil {
+		return "", fmt.Errorf("failed to write JWT signing key: %w", err)
+	}
+
+	// Double-check permissions (some systems might ignore mode in WriteFile)
+	if err := os.Chmod(keyPath, JWTKeyPerm); err != nil {
+		return "", fmt.Errorf("failed to set JWT signing key permissions: %w", err)
+	}
+
+	log.Info("JWT signing key generated and stored", "path", keyPath)
+	return key, nil
+}
+
+// generateJWTSigningKey generates a cryptographically secure random signing key
+func generateJWTSigningKey() (string, error) {
+	keyBytes := make([]byte, JWTKeyBytes)
+	if _, err := rand.Read(keyBytes); err != nil {
+		return "", fmt.Errorf("failed to generate random bytes: %w", err)
+	}
+
+	// Encode to base64 for easy storage and handling
+	key := base64.StdEncoding.EncodeToString(keyBytes)
+	return key, nil
+}
+