Add Google OAuth authentication infrastructure

- Add passport, passport-google-oauth20, jsonwebtoken, cookie-parser, uuid deps
- Create config/auth.js with JWT, cookie, and OAuth configuration
- Create models/user.js with MongoDB user model and indexes
- Create middleware/passport.js with Google OAuth strategy
- Create middleware/auth.js with requireAuth middleware and sliding window refresh
- Create routes/auth.js with OAuth flow endpoints
- Update server.js to integrate auth, protect all data endpoints (except /health)
- Configure CORS for cookie-based authentication

models/user.js

@@ -0,0 +1,129 @@
+const { ObjectId } = require('mongodb');
+
+const USER_COLLECTION = 'users';
+
+/**
+ * Find or create a user based on Google OAuth profile
+ * Uses upsert pattern to handle both new and returning users
+ *
+ * @param {Db} db - MongoDB database instance
+ * @param {Object} profile - Google OAuth profile
+ * @param {string} profile.id - Google's unique user ID
+ * @param {string} profile.displayName - User's display name
+ * @param {Array} profile.emails - Array of email objects
+ * @param {Array} profile.photos - Array of photo objects
+ * @returns {Promise<Object>} User document
+ */
+async function findOrCreateUser(db, profile) {
+  const now = new Date();
+
+  const result = await db.collection(USER_COLLECTION).findOneAndUpdate(
+    { googleId: profile.id },
+    {
+      $set: {
+        email: profile.emails[0].value,
+        name: profile.displayName,
+        picture: profile.photos?.[0]?.value || null,
+        lastLoginAt: now
+      },
+      $inc: { loginCount: 1 },
+      $setOnInsert: {
+        googleId: profile.id,
+        isActive: true,
+        role: 'user',
+        createdAt: now,
+        loginCount: 0 // Will be incremented to 1 by $inc
+      }
+    },
+    {
+      upsert: true,
+      returnDocument: 'after'
+    }
+  );
+
+  return result;
+}
+
+/**
+ * Find a user by Google ID
+ *
+ * @param {Db} db - MongoDB database instance
+ * @param {string} googleId - Google's unique user ID
+ * @returns {Promise<Object|null>} User document or null
+ */
+async function findByGoogleId(db, googleId) {
+  return await db.collection(USER_COLLECTION).findOne({ googleId });
+}
+
+/**
+ * Find a user by MongoDB ObjectId
+ *
+ * @param {Db} db - MongoDB database instance
+ * @param {string|ObjectId} id - User's MongoDB _id
+ * @returns {Promise<Object|null>} User document or null
+ */
+async function findById(db, id) {
+  // Convert string to ObjectId if needed
+  const objectId = typeof id === 'string' ? new ObjectId(id) : id;
+  return await db.collection(USER_COLLECTION).findOne({ _id: objectId });
+}
+
+/**
+ * Enable or disable a user account
+ *
+ * @param {Db} db - MongoDB database instance
+ * @param {string|ObjectId} id - User's MongoDB _id
+ * @param {boolean} isActive - New active status
+ * @returns {Promise<Object>} Update result
+ */
+async function setUserActive(db, id, isActive) {
+  // Convert string to ObjectId if needed
+  const objectId = typeof id === 'string' ? new ObjectId(id) : id;
+
+  const result = await db.collection(USER_COLLECTION).findOneAndUpdate(
+    { _id: objectId },
+    { $set: { isActive } },
+    { returnDocument: 'after' }
+  );
+
+  return result;
+}
+
+/**
+ * Create required indexes for the users collection
+ * Should be called once during application startup
+ *
+ * @param {Db} db - MongoDB database instance
+ * @returns {Promise<void>}
+ */
+async function createIndexes(db) {
+  const collection = db.collection(USER_COLLECTION);
+
+  // Unique index on googleId for OAuth lookups
+  await collection.createIndex(
+    { googleId: 1 },
+    { unique: true }
+  );
+
+  // Unique index on email for user identification
+  await collection.createIndex(
+    { email: 1 },
+    { unique: true }
+  );
+
+  // Compound index for querying active users sorted by last login
+  await collection.createIndex(
+    { isActive: 1, lastLoginAt: -1 }
+  );
+
+  console.log('User collection indexes created successfully');
+}
+
+module.exports = {
+  USER_COLLECTION,
+  findOrCreateUser,
+  findByGoogleId,
+  findById,
+  setUserActive,
+  createIndexes
+};