Initial LinkedSign platform

backend/src/middlewares/authRateLimiter.js

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+const rateLimit = require('express-rate-limit');
+
+const authRateLimiter = rateLimit({
+  windowMs: 15 * 60 * 1000,
+  max: 20,
+  standardHeaders: true,
+  legacyHeaders: false,
+  message: {
+    success: false,
+    data: null,
+    error: 'Too many login attempts. Please try again later.',
+  },
+});
+
+module.exports = authRateLimiter;

backend/src/middlewares/authenticate.js

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+const { verify } = require('../utils/jwt');
+
+const authenticate = (req, res, next) => {
+  const authHeader = req.headers['authorization'];
+  if (!authHeader || !authHeader.startsWith('Bearer ')) {
+    return res.status(401).json({ success: false, data: null, error: 'Authorization token required.' });
+  }
+
+  const token = authHeader.slice(7);
+  try {
+    const decoded = verify(token);
+    req.user = { id: decoded.sub, email: decoded.email, role: decoded.role, name: decoded.name };
+    return next();
+  } catch {
+    return res.status(401).json({ success: false, data: null, error: 'Invalid or expired token.' });
+  }
+};
+
+module.exports = authenticate;

backend/src/middlewares/errorHandler.js

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+const { sendError } = require('../utils/apiResponse');
+
+const errorHandler = (err, req, res, next) => {
+  if (res.headersSent) {
+    return next(err);
+  }
+
+  const statusCode = err.statusCode || 500;
+  if (statusCode >= 500) {
+    console.error(`[ERROR ${statusCode}]`, err.message);
+    console.error(err.stack?.split('\n').slice(0, 6).join('\n'));
+  }
+  const message = err.code
+    ? (err.message || 'Request error')
+    : (statusCode >= 500 ? 'Internal server error' : err.message || 'Request error');
+
+  if (err.code) {
+    return res.status(statusCode).json({
+      success: false,
+      data: err.data || null,
+      error: message,
+      code: err.code,
+    });
+  }
+
+  return sendError(res, message, statusCode);
+};
+
+module.exports = errorHandler;

backend/src/middlewares/fileValidator.js

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+const path = require('path');
+
+const MAX_FILE_SIZE = 10 * 1024 * 1024;
+
+const fileValidator = (req, res, next) => {
+  const file = req.file;
+
+  if (!file) {
+    const error = new Error('Invalid file upload');
+    error.statusCode = 400;
+    return next(error);
+  }
+
+  const extension = path.extname(file.originalname || '').toLowerCase();
+  const isPdfMimeType = file.mimetype === 'application/pdf';
+  const isPdfExtension = extension === '.pdf';
+  const isValidSize = typeof file.size === 'number' && file.size <= MAX_FILE_SIZE;
+
+  if (!isPdfMimeType || !isPdfExtension || !isValidSize) {
+    const error = new Error('Invalid file upload');
+    error.statusCode = 400;
+    return next(error);
+  }
+
+  return next();
+};
+
+module.exports = fileValidator;

backend/src/middlewares/notFound.js

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+const { sendError } = require('../utils/apiResponse');
+
+const notFound = (req, res) => {
+  return sendError(res, `Route not found: ${req.method} ${req.originalUrl}`, 404);
+};
+
+module.exports = notFound;