Add configuration options to disable optional functionalities

Implemented feature toggles for:
- Authentication system (auth_enabled)
- Tamper-evident logging (tamper_logging_enabled)
- Clustering/gossip (clustering_enabled)
- Rate limiting (rate_limiting_enabled)
- Revision history (revision_history_enabled)

All features are enabled by default to maintain backward compatibility.
When disabled, features are gracefully skipped to reduce overhead.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

main.go

@@ -294,6 +294,13 @@ type Config struct {
 	BackupSchedule  string `yaml:"backup_schedule"`   // Cron schedule format
 	BackupPath      string `yaml:"backup_path"`       // Directory to store backups
 	BackupRetention int    `yaml:"backup_retention"`  // Days to keep backups
+	
+	// Feature toggles for optional functionalities
+	AuthEnabled            bool `yaml:"auth_enabled"`             // Enable/disable authentication system
+	TamperLoggingEnabled   bool `yaml:"tamper_logging_enabled"`   // Enable/disable tamper-evident logging
+	ClusteringEnabled      bool `yaml:"clustering_enabled"`       // Enable/disable clustering/gossip
+	RateLimitingEnabled    bool `yaml:"rate_limiting_enabled"`    // Enable/disable rate limiting
+	RevisionHistoryEnabled bool `yaml:"revision_history_enabled"` // Enable/disable revision history
 }
 
 // Server represents the KVS node
@@ -652,6 +659,12 @@ func (s *Server) checkResourcePermission(authCtx *AuthContext, resourceKey strin
 func (s *Server) authMiddleware(requiredScopes []string, resourceKeyExtractor func(*http.Request) string, operation string) func(http.HandlerFunc) http.HandlerFunc {
 	return func(next http.HandlerFunc) http.HandlerFunc {
 		return func(w http.ResponseWriter, r *http.Request) {
+			// Skip authentication if disabled
+			if !s.config.AuthEnabled {
+				next(w, r)
+				return
+			}
+			
 			// Authenticate request
 			authCtx, err := s.authenticateRequest(r)
 			if err != nil {
@@ -1082,6 +1095,12 @@ func (s *Server) checkRateLimit(userUUID string) (bool, error) {
 // rateLimitMiddleware is the HTTP middleware that enforces rate limiting
 func (s *Server) rateLimitMiddleware(next http.HandlerFunc) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
+		// Skip rate limiting if disabled
+		if !s.config.RateLimitingEnabled {
+			next(w, r)
+			return
+		}
+		
 		// Extract auth context to get user UUID
 		authCtx, ok := r.Context().Value("auth").(*AuthContext)
 		if !ok || authCtx == nil {
@@ -1148,8 +1167,8 @@ func (s *Server) isActionLogged(action string) bool {
 
 // createTamperLogEntry creates a new tamper-evident log entry
 func (s *Server) createTamperLogEntry(action, userUUID, resource string) *TamperLogEntry {
-	if !s.isActionLogged(action) {
-		return nil // Action not configured for logging
+	if !s.config.TamperLoggingEnabled || !s.isActionLogged(action) {
+		return nil // Tamper logging disabled or action not configured for logging
 	}
 	
 	timestamp := time.Now().UTC().Format(time.RFC3339)
@@ -1486,6 +1505,13 @@ func defaultConfig() *Config {
 		BackupSchedule:  "0 0 * * *", // Daily at midnight
 		BackupPath:      "./backups",
 		BackupRetention: 7, // Keep backups for 7 days
+		
+		// Default feature toggle settings (all enabled by default)
+		AuthEnabled:            true,
+		TamperLoggingEnabled:   true,
+		ClusteringEnabled:      true,
+		RateLimitingEnabled:    true,
+		RevisionHistoryEnabled: true,
 	}
 }
 
@@ -2100,8 +2126,8 @@ func (s *Server) Start() error {
 	// Start gossip and sync routines
 	s.startBackgroundTasks()
 
-	// Try to join cluster if seed nodes are configured
-	if len(s.config.SeedNodes) > 0 {
+	// Try to join cluster if seed nodes are configured and clustering is enabled
+	if s.config.ClusteringEnabled && len(s.config.SeedNodes) > 0 {
 		go s.bootstrap()
 	}
 
@@ -2131,15 +2157,18 @@ func (s *Server) Stop() error {
 
 // Background tasks (gossip, sync, Merkle tree rebuild, etc.)
 func (s *Server) startBackgroundTasks() {
-	// Start gossip routine
-	s.wg.Add(1)
-	go s.gossipRoutine()
+	// Start clustering-related routines only if clustering is enabled
+	if s.config.ClusteringEnabled {
+		// Start gossip routine
+		s.wg.Add(1)
+		go s.gossipRoutine()
 
-	// Start sync routine (now Merkle-based)
-	s.wg.Add(1)
-	go s.syncRoutine()
+		// Start sync routine (now Merkle-based)
+		s.wg.Add(1)
+		go s.syncRoutine()
+	}
 
-	// Start Merkle tree rebuild routine
+	// Start Merkle tree rebuild routine (always needed for data integrity)
 	s.wg.Add(1)
 	go s.merkleTreeRebuildRoutine()
 }
@@ -3194,6 +3223,12 @@ func (s *Server) createTokenHandler(w http.ResponseWriter, r *http.Request) {
 
 // getRevisionHistoryHandler handles GET /api/data/{key}/history
 func (s *Server) getRevisionHistoryHandler(w http.ResponseWriter, r *http.Request) {
+	// Check if revision history is enabled
+	if !s.config.RevisionHistoryEnabled {
+		http.Error(w, "Revision history is disabled", http.StatusServiceUnavailable)
+		return
+	}
+	
 	vars := mux.Vars(r)
 	key := vars["key"]
 
@@ -3224,6 +3259,12 @@ func (s *Server) getRevisionHistoryHandler(w http.ResponseWriter, r *http.Reques
 
 // getSpecificRevisionHandler handles GET /api/data/{key}/history/{revision}
 func (s *Server) getSpecificRevisionHandler(w http.ResponseWriter, r *http.Request) {
+	// Check if revision history is enabled
+	if !s.config.RevisionHistoryEnabled {
+		http.Error(w, "Revision history is disabled", http.StatusServiceUnavailable)
+		return
+	}
+	
 	vars := mux.Vars(r)
 	key := vars["key"]
 	revisionStr := vars["revision"]