Implement authentication filter to protect private pages

[aolguin89]

User Story

As a system administrator
I want to protect private pages from unauthorized access
So that only authenticated users can access restricted areas

Description

Create a Servlet Filter that intercepts requests to protected pages and validates session. Redirects to login if not authenticated.

Tasks

• Create AuthenticationFilter.java in filter/ package
• Implement doFilter() to check session
• Configure filter in web.xml for /WEB-INF/views/*
• Define public URLs that don't require authentication
• Redirect to login with original URL parameter

Acceptance Criteria

• Unauthenticated users cannot access /WEB-INF/views/*
• Filter redirects to login page
• After login, user returns to originally requested page
• Public pages (login, index) remain accessible
• Authenticated users pass through filter