JwtAuthenticationFilter.java

package com.flogin.backend.config;

import com.flogin.backend.service.auth.IUserDetailService;
import jakarta.servlet.FilterChain;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import org.springframework.security.core.GrantedAuthority;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.web.authentication.WebAuthenticationDetailsSource;
import org.springframework.stereotype.Component;
import org.springframework.web.filter.OncePerRequestFilter;

import java.io.IOException;
import java.util.stream.Collectors;

@Component
@RequiredArgsConstructor
@Slf4j
public class JwtAuthenticationFilter extends OncePerRequestFilter {

    private final JwtUtil jwtUtil;
    private final IUserDetailService userDetailsService;

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {

        String authHeader = request.getHeader("Authorization");

        if (authHeader == null || !authHeader.startsWith("Bearer ")) {
            filterChain.doFilter(request, response);
            return;
        }

        String token = authHeader.substring(7);
        String username = null;

        try {
            // Extract username AND validate in one step - safe against all JWT errors
            username = jwtUtil.getUsernameFromToken(token);  // This validates implicitly

            if (username != null && SecurityContextHolder.getContext().getAuthentication() == null) {
                UserDetails userDetails = userDetailsService.loadUserByUsername(username);

                UsernamePasswordAuthenticationToken authToken = new UsernamePasswordAuthenticationToken(userDetails, null, userDetails.getAuthorities());
                authToken.setDetails(new WebAuthenticationDetailsSource().buildDetails(request));
                SecurityContextHolder.getContext().setAuthentication(authToken);

                log.debug("Authorized user: {} with authorities: {}", username, userDetails.getAuthorities().stream().map(GrantedAuthority::getAuthority).collect(Collectors.joining(", ")));
            }
        } catch (Exception e) {  // Catches MalformedJwtException, ExpiredJwtException, SignatureException, etc.
            log.warn("Invalid JWT token: {}", e.getMessage());
            sendUnauthorizedResponse(response, "Invalid or expired JWT token");
            return;
        }

        filterChain.doFilter(request, response);
    }

    private void sendUnauthorizedResponse(HttpServletResponse response, String message) throws IOException {
        response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
        response.setContentType("application/json;charset=UTF-8");
        response.getWriter().write("{\"error\":\"" + message + "\"}");
    }

}