"Why is my API returning HTML error pages?!" I stared at my console in disbelief. My React frontend was trying to parse JSON, but Spring Security was happily serving up a Whitelabel Error Page for failed authentication attempts. This took me 3 hours to fix. Let me show you how to make Spring Security play nice with modern frontends. 🎨✨
Ever wondered why sometimes your Spring Boot exceptions are caught by @RestControllerAdvice and other times they're not? Or why your custom AccessDeniedHandler returns 403 before your controller even executes? I spent hours debugging this mystery until I understood Spring Boot's two-tier exception handling architecture. Let me save you the confusion. 🎯
"My login endpoint is returning 403 Forbidden! But I configured it as .permitAll() in SecurityConfig! Why is the JwtFilter still blocking it?" I spent 2 hours debugging this. Turns out, I had a fundamental misunderstanding of how Spring Security works. The JwtFilter doesn't "skip" endpoints - it runs on EVERYTHING. Let me explain the magic. 🎩✨
"I just added spring-boot-starter-security to my pom.xml and now ALL my endpoints return 401 Unauthorized! I didn't write any security code - why is this happening?" This is Spring Security's "secure by default" philosophy at work. Let's understand why this design choice makes sense and how to configure it.