backend: Add request validator middleware for login requests

backend/src/middlewares/request-validators/auth-validator.middleware.ts

@@ -0,0 +1,27 @@
+import { Request, Response, NextFunction } from 'express';
+import { z } from 'zod';
+
+const LoginRequestSchema = z.object({
+	username: z.string().min(4, 'Username must be at least 4 characters long'),
+	password: z.string().min(4, 'Password must be at least 4 characters long')
+});
+
+export const validateLoginRequest = (req: Request, res: Response, next: NextFunction) => {
+	const { success, error, data } = LoginRequestSchema.safeParse(req.body);
+
+	if (!success) {
+		const errors = error.errors.map((error) => ({
+			field: error.path.join('.'),
+			message: error.message
+		}));
+
+		return res.status(422).json({
+			error: 'Unprocessable Entity',
+			message: 'Invalid request body',
+			details: errors
+		});
+	}
+
+	req.body = data;
+	next();
+};