Add SecurityAuthFailureHandler for better handling of authentication and access failures; update SecurityConfig to integrate the new handler.

backend/src/main/java/com/alttd/altitudeweb/config/SecurityAuthFailureHandler.java

@@ -0,0 +1,36 @@
+package com.alttd.altitudeweb.config;
+
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.security.access.AccessDeniedException;
+import org.springframework.security.core.AuthenticationException;
+import org.springframework.security.web.AuthenticationEntryPoint;
+import org.springframework.security.web.access.AccessDeniedHandler;
+import org.springframework.stereotype.Component;
+
+import java.io.IOException;
+
+@Slf4j
+@Component
+public class SecurityAuthFailureHandler implements AccessDeniedHandler, AuthenticationEntryPoint {
+    
+    @Override
+    public void handle(HttpServletRequest request, HttpServletResponse response, 
+                      AccessDeniedException accessDeniedException) throws IOException {
+        log.warn("Access denied: User '{}' attempted to access '{}' without proper permissions",
+                  request.getUserPrincipal() != null ? request.getUserPrincipal().getName() : "unknown", 
+                  request.getRequestURI());
+        
+        response.sendError(HttpServletResponse.SC_FORBIDDEN, "Access Denied");
+    }
+    
+    @Override
+    public void commence(HttpServletRequest request, HttpServletResponse response, 
+                        AuthenticationException authException) throws IOException {
+        log.warn("Authentication failure: Unauthenticated user attempted to access secured endpoint '{}'",
+                  request.getRequestURI());
+        
+        response.sendError(HttpServletResponse.SC_UNAUTHORIZED, "Authentication Required");
+    }
+}