refactor: enhance security and performance in configuration and API routes

- Update Content Security Policy (CSP) in next.config.ts to avoid `unsafe-eval` in production, improving security against XSS attacks.
- Refactor API routes to enforce admin authentication and session validation, ensuring secure access to sensitive endpoints.
- Optimize analytics data retrieval by using database aggregation instead of loading all records into memory, improving performance and reducing memory usage.
- Implement session token creation and verification for better session management and security across the application.
- Enhance error handling and input validation in various API routes to ensure robustness and prevent potential issues.

app/api/auth/validate/route.ts

@@ -1,4 +1,5 @@
 import { NextRequest, NextResponse } from 'next/server';
+import { verifySessionToken } from '@/lib/auth';
 
 export async function POST(request: NextRequest) {
   try {
@@ -20,70 +21,26 @@ export async function POST(request: NextRequest) {
       );
     }
 
-    // Decode and validate session token
-    try {
-      const decodedJson = atob(sessionToken);
-      const sessionData = JSON.parse(decodedJson);
-
-      // Validate session data structure
-      if (!sessionData.timestamp || !sessionData.random || !sessionData.ip || !sessionData.userAgent) {
-        return new NextResponse(
-          JSON.stringify({ valid: false, error: 'Invalid session token structure' }),
-          { status: 401, headers: { 'Content-Type': 'application/json' } }
-        );
-      }
-
-      // Check if session is still valid (2 hours)
-      const sessionTime = sessionData.timestamp;
-      const now = Date.now();
-      const sessionDuration = 2 * 60 * 60 * 1000; // 2 hours
-
-      if (now - sessionTime > sessionDuration) {
-        return new NextResponse(
-          JSON.stringify({ valid: false, error: 'Session expired' }),
-          { status: 401, headers: { 'Content-Type': 'application/json' } }
-        );
-      }
-
-      // Validate IP address (optional, but good security practice)
-      const currentIp = request.headers.get('x-forwarded-for') || request.headers.get('x-real-ip') || 'unknown';
-      if (sessionData.ip !== currentIp) {
-        // Log potential session hijacking attempt
-        console.warn(`Session IP mismatch: expected ${sessionData.ip}, got ${currentIp}`);
-        return new NextResponse(
-          JSON.stringify({ valid: false, error: 'Session validation failed' }),
-          { status: 401, headers: { 'Content-Type': 'application/json' } }
-        );
-      }
-
-      // Validate User-Agent (optional)
-      const currentUserAgent = request.headers.get('user-agent') || 'unknown';
-      if (sessionData.userAgent !== currentUserAgent) {
-        console.warn(`Session User-Agent mismatch`);
-        return new NextResponse(
-          JSON.stringify({ valid: false, error: 'Session validation failed' }),
-          { status: 401, headers: { 'Content-Type': 'application/json' } }
-        );
-      }
-
+    const valid = verifySessionToken(request, sessionToken);
+    if (!valid) {
       return new NextResponse(
-        JSON.stringify({ valid: true, message: 'Session valid' }),
-        {
-          status: 200,
-          headers: {
-            'Content-Type': 'application/json',
-            'X-Content-Type-Options': 'nosniff',
-            'X-Frame-Options': 'DENY',
-            'X-XSS-Protection': '1; mode=block'
-          }
-        }
-      );
-    } catch {
-      return new NextResponse(
-        JSON.stringify({ valid: false, error: 'Invalid session token format' }),
+        JSON.stringify({ valid: false, error: 'Session expired or invalid' }),
         { status: 401, headers: { 'Content-Type': 'application/json' } }
       );
     }
+
+    return new NextResponse(
+      JSON.stringify({ valid: true, message: 'Session valid' }),
+      {
+        status: 200,
+        headers: {
+          'Content-Type': 'application/json',
+          'X-Content-Type-Options': 'nosniff',
+          'X-Frame-Options': 'DENY',
+          'X-XSS-Protection': '1; mode=block'
+        }
+      }
+    );
   } catch {
     return new NextResponse(
       JSON.stringify({ valid: false, error: 'Internal server error' }),