feat: implement cache layer, CSP improvements, and database performance optimizations

- Add Redis cache implementation with LRU eviction
- Enhance Content Security Policy with nonce generation
- Optimize database queries with connection pooling
- Add cache invalidation API endpoints
- Improve security monitoring performance

app/api/admin/cache/stats/route.ts

@@ -0,0 +1,157 @@
+/**
+ * Cache Statistics API Endpoint
+ *
+ * Provides comprehensive cache performance metrics and health status
+ * for monitoring Redis + in-memory cache performance.
+ */
+
+import { NextResponse } from "next/server";
+import { getServerSession } from "next-auth";
+import { authOptions } from "../../../../../lib/auth";
+import { Cache } from "../../../../../lib/cache";
+import {
+  AuditOutcome,
+  AuditSeverity,
+  createAuditMetadata,
+  SecurityEventType,
+} from "../../../../../lib/securityAuditLogger";
+import { enhancedSecurityLog } from "../../../../../lib/securityMonitoring";
+
+export async function GET() {
+  try {
+    const session = await getServerSession(authOptions);
+
+    if (!session?.user) {
+      await enhancedSecurityLog(
+        SecurityEventType.AUTHORIZATION,
+        "cache_stats_access_denied",
+        AuditOutcome.BLOCKED,
+        {
+          metadata: createAuditMetadata({
+            endpoint: "/api/admin/cache/stats",
+            reason: "not_authenticated",
+          }),
+        },
+        AuditSeverity.MEDIUM,
+        "Unauthenticated access attempt to cache stats endpoint"
+      );
+
+      return NextResponse.json(
+        { success: false, error: "Authentication required" },
+        { status: 401 }
+      );
+    }
+
+    if (session.user.role !== "ADMIN") {
+      await enhancedSecurityLog(
+        SecurityEventType.AUTHORIZATION,
+        "cache_stats_access_denied",
+        AuditOutcome.BLOCKED,
+        {
+          userId: session.user.id,
+          companyId: session.user.companyId,
+          metadata: createAuditMetadata({
+            endpoint: "/api/admin/cache/stats",
+            userRole: session.user.role,
+            reason: "insufficient_privileges",
+          }),
+        },
+        AuditSeverity.HIGH,
+        "Non-admin user attempted to access cache stats"
+      );
+
+      return NextResponse.json(
+        { success: false, error: "Admin access required" },
+        { status: 403 }
+      );
+    }
+
+    // Get cache statistics and health information
+    const [stats, healthCheck] = await Promise.all([
+      Cache.getStats(),
+      Cache.healthCheck(),
+    ]);
+
+    const response = {
+      success: true,
+      data: {
+        performance: {
+          hits: stats.hits,
+          misses: stats.misses,
+          sets: stats.sets,
+          deletes: stats.deletes,
+          errors: stats.errors,
+          hitRate: Number((stats.hitRate * 100).toFixed(2)), // Convert to percentage
+          redisHits: stats.redisHits,
+          memoryHits: stats.memoryHits,
+        },
+        health: {
+          redis: {
+            connected: healthCheck.redis.connected,
+            latency: healthCheck.redis.latency,
+            error: healthCheck.redis.error,
+          },
+          memory: {
+            available: healthCheck.memory.available,
+            size: healthCheck.memory.size,
+            valid: healthCheck.memory.valid,
+            expired: healthCheck.memory.expired,
+          },
+          overall: {
+            available: healthCheck.overall.available,
+            fallbackMode: healthCheck.overall.fallbackMode,
+          },
+        },
+        configuration: {
+          redisAvailable: stats.redisAvailable,
+          fallbackActive: !stats.redisAvailable,
+        },
+        timestamp: new Date().toISOString(),
+      },
+    };
+
+    // Log successful access
+    await enhancedSecurityLog(
+      SecurityEventType.PLATFORM_ADMIN,
+      "cache_stats_accessed",
+      AuditOutcome.SUCCESS,
+      {
+        userId: session.user.id,
+        companyId: session.user.companyId,
+        metadata: createAuditMetadata({
+          endpoint: "/api/admin/cache/stats",
+          hitRate: response.data.performance.hitRate,
+          redisConnected: response.data.health.redis.connected,
+        }),
+      },
+      AuditSeverity.INFO,
+      "Cache statistics accessed by admin"
+    );
+
+    return NextResponse.json(response);
+  } catch (error) {
+    console.error("[Cache Stats API] Error:", error);
+
+    await enhancedSecurityLog(
+      SecurityEventType.API_SECURITY,
+      "cache_stats_error",
+      AuditOutcome.FAILURE,
+      {
+        metadata: createAuditMetadata({
+          endpoint: "/api/admin/cache/stats",
+          error: error instanceof Error ? error.message : "Unknown error",
+        }),
+      },
+      AuditSeverity.HIGH,
+      "Cache stats API encountered an error"
+    );
+
+    return NextResponse.json(
+      {
+        success: false,
+        error: "Internal server error",
+      },
+      { status: 500 }
+    );
+  }
+}