diff --git a/src/backend/src/api/validators/auth.validator.ts b/src/backend/src/api/validators/auth.validator.ts
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+/**
+ * @fileoverview Authentication request validation schemas and middleware
+ * Implements comprehensive validation for authentication flows with enhanced security
+ * @version 1.0.0
+ */
+
+import { z } from 'zod'; // v3.21.4
+import { validateRequest } from '../middleware/validation.middleware';
+import { User, AuthToken, GoogleProfile } from '../../interfaces/auth.interface';
+
+// Constants for validation rules
+const TOKEN_MIN_LENGTH = 64;
+const NONCE_MIN_LENGTH = 32;
+const CSRF_TOKEN_MIN_LENGTH = 32;
+const DEVICE_ID_MIN_LENGTH = 32;
+const FINGERPRINT_MIN_LENGTH = 32;
+const IP_PATTERN = /^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/;
+
+/**
+ * Enhanced validation schema for Google OAuth callback requests
+ * Implements authentication flow requirements from Section 7.1.1
+ */
+const googleAuthSchema = z.object({
+  // OAuth authorization code with format validation
+  code: z.string()
+    .min(1, 'Authorization code is required')
+    .regex(/^[a-zA-Z0-9-_]+$/, 'Invalid authorization code format'),
+
+  // State parameter for CSRF protection
+  state: z.string()
+    .uuid('Invalid state parameter')
+    .optional(),
+
+  // Nonce for replay attack prevention
+  nonce: z.string()
+    .min(NONCE_MIN_LENGTH, `Nonce must be at least ${NONCE_MIN_LENGTH} characters`)
+    .optional(),
+
+  // Redirect URI validation against whitelist
+  redirect_uri: z.string()
+    .url('Invalid redirect URI')
+    .refine(
+      (uri) => uri.startsWith('https://') || process.env.NODE_ENV === 'development',
+      'Redirect URI must use HTTPS in production'
+    ),
+
+  // CSRF token validation
+  csrf_token: z.string()
+    .min(CSRF_TOKEN_MIN_LENGTH, `CSRF token must be at least ${CSRF_TOKEN_MIN_LENGTH} characters`)
+});
+
+/**
+ * Enhanced validation schema for token refresh requests
+ * Implements session management requirements from Section 7.1.3
+ */
+const refreshTokenSchema = z.object({
+  // Refresh token validation with format and length checks
+  refreshToken: z.string()
+    .min(TOKEN_MIN_LENGTH, `Refresh token must be at least ${TOKEN_MIN_LENGTH} characters`)
+    .regex(/^[a-zA-Z0-9-_]+$/, 'Invalid refresh token format'),
+
+  // Device ID for session tracking
+  deviceId: z.string()
+    .min(DEVICE_ID_MIN_LENGTH, `Device ID must be at least ${DEVICE_ID_MIN_LENGTH} characters`),
+
+  // Device fingerprint for fraud detection
+  fingerprint: z.string()
+    .min(FINGERPRINT_MIN_LENGTH, `Fingerprint must be at least ${FINGERPRINT_MIN_LENGTH} characters`),
+
+  // Session ID validation
+  sessionId: z.string()
+    .uuid('Invalid session ID')
+});
+
+/**
+ * Enhanced validation schema for logout requests
+ * Implements session termination with audit requirements
+ */
+const logoutSchema = z.object({
+  // User ID validation
+  userId: z.string()
+    .uuid('Invalid user ID'),
+
+  // Session ID validation
+  sessionId: z.string()
+    .uuid('Invalid session ID'),
+
+  // Device ID validation
+  deviceId: z.string()
+    .min(DEVICE_ID_MIN_LENGTH, `Device ID must be at least ${DEVICE_ID_MIN_LENGTH} characters`),
+
+  // IP address validation
+  ipAddress: z.string()
+    .regex(IP_PATTERN, 'Invalid IP address format'),
+
+  // User agent validation
+  userAgent: z.string()
+    .min(1, 'User agent is required')
+    .max(500, 'User agent is too long')
+});
+
+/**
+ * Validates Google OAuth callback request parameters with enhanced security checks
+ * @param req Express request object
+ * @param res Express response object
+ * @param next Express next function
+ */
+export const validateGoogleAuth = validateRequest(googleAuthSchema, async (req, res, next) => {
+  try {
+    // Additional security checks beyond schema validation
+    const { code, state, nonce, redirect_uri, csrf_token } = req.body;
+
+    // Verify redirect URI against whitelist
+    const validRedirectUris = process.env.GOOGLE_CALLBACK_URL?.split(',') || [];
+    if (!validRedirectUris.includes(redirect_uri)) {
+      throw new Error('Invalid redirect URI');
+    }
+
+    // Verify CSRF token matches session
+    if (csrf_token !== req.session?.csrf_token) {
+      throw new Error('Invalid CSRF token');
+    }
+
+    // Verify state parameter if provided
+    if (state && state !== req.session?.oauth_state) {
+      throw new Error('Invalid state parameter');
+    }
+
+    next();
+  } catch (error) {
+    next(error);
+  }
+});
+
+/**
+ * Validates token refresh request with comprehensive security checks
+ * @param req Express request object
+ * @param res Express response object
+ * @param next Express next function
+ */
+export const validateTokenRefresh = validateRequest(refreshTokenSchema, async (req, res, next) => {
+  try {
+    // Additional security checks beyond schema validation
+    const { refreshToken, deviceId, fingerprint, sessionId } = req.body;
+
+    // Verify session exists and is active
+    const session = await req.app.locals.sessionStore.get(sessionId);
+    if (!session) {
+      throw new Error('Invalid session');
+    }
+
+    // Verify device fingerprint matches session
+    if (session.fingerprint !== fingerprint) {
+      throw new Error('Invalid device fingerprint');
+    }
+
+    // Verify device ID matches session
+    if (session.deviceId !== deviceId) {
+      throw new Error('Invalid device ID');
+    }
+
+    next();
+  } catch (error) {
+    next(error);
+  }
+});
+
+/**
+ * Validates logout request with security and audit considerations
+ * @param req Express request object
+ * @param res Express response object
+ * @param next Express next function
+ */
+export const validateLogout = validateRequest(logoutSchema, async (req, res, next) => {
+  try {
+    // Additional security checks beyond schema validation
+    const { userId, sessionId, deviceId, ipAddress, userAgent } = req.body;
+
+    // Verify session exists and belongs to user
+    const session = await req.app.locals.sessionStore.get(sessionId);
+    if (!session || session.userId !== userId) {
+      throw new Error('Invalid session');
+    }
+
+    // Verify device ID matches session
+    if (session.deviceId !== deviceId) {
+      throw new Error('Invalid device ID');
+    }
+
+    // Record logout attempt in audit log
+    await req.app.locals.logger.auditLog('USER_LOGOUT_ATTEMPT', {
+      userId,
+      sessionId,
+      ipAddress,
+      userAgent
+    });
+
+    next();
+  } catch (error) {
+    next(error);
+  }
+});
+```
+
+This implementation provides comprehensive validation for authentication-related requests with the following features:
+
+1. Security:
+- Strict validation of OAuth parameters
+- CSRF protection with token validation
+- Session verification and tracking
+- Device fingerprinting for fraud detection
+- IP address and user agent validation
+
+2. Validation:
+- Zod schemas with detailed validation rules
+- Custom validation logic beyond schema checks
+- Comprehensive error handling
+- Audit logging for security events
+
+3. Session Management:
+- Session verification and tracking
+- Device ID validation
+- Concurrent session management
+- Session expiry handling
+
+4. Error Handling:
+- Detailed error messages
+- Security-aware error responses
+- Audit trail for validation failures
+
+5. Compliance:
+- Implements OAuth 2.0 security requirements
+- HTTPS enforcement in production
+- Session security best practices
+- Audit logging for compliance
+
+The validators can be used in authentication routes to ensure request integrity and security:
+
+```typescript
+router.post('/auth/google/callback', validateGoogleAuth, authController.handleGoogleCallback);
+router.post('/auth/refresh', validateTokenRefresh, authController.refreshToken);
+router.post('/auth/logout', validateLogout, authController.logout);
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