A New Collection of Thoughtful Learning Apps — Now Available on iOS & Android

By
Image
I’m excited to share a set of mobile apps I’ve recently completed and published on both the Google Play Store and the Apple App Store. These apps are designed with a simple goal in mind: to make meaningful, structured content more accessible, whether you’re studying theology or improving your English vocabulary. 📱 Now Available on Both Platforms All apps are live and available for download: Google Play Developer Page: https://play.google.com/store/apps/dev?id=5835943159853189043 Apple App Store Developer Page: https://apps.apple.com/ca/developer/q-z-l-corp/id1888794100 📖 Theology & Confession Study Apps For those interested in Reformed theology and classical Christian teachings, I’ve developed a series of apps that present foundational texts in a clean, focused reading format: The Belgic Confession Canons of Dort Heidelberg Catechism Westminster Shorter Catechism Each app is designed to provide a distraction-free experience, making it easier to read, reflect, and revisit these im...
Post a Comment

Spring Security SSO Series

By

Spring Security SSO Series

This series is a deep dive into Single Sign-On (SSO) using Spring Security. It focuses not only on configuration, but also on how Spring Security actually works internally and how to debug real-world authentication and authorization issues.

If you often encounter unexplained 401 or 403 errors, this series is written for you.

📘 Part 1 — SSO Fundamentals

  1. Understanding SSO: Concepts and Protocols

    A clear explanation of SSO, OAuth2, OpenID Connect, tokens, and trust boundaries — without vendor-specific noise.

🔌 Part 2 — Integrating SSO with Spring

  1. Integrating Keycloak with Spring Boot — A Practical Guide

    Step-by-step integration of Keycloak with Spring Boot using OAuth2 and OIDC.

  2. SSO for Spring WebFlux — Reactive Authentication and Authorization

    How reactive authentication works in WebFlux and how it differs from traditional Servlet-based Spring Security.

🧠 Part 3 — How Spring Security Really Works

  1. How to Debug Spring Security Filter Chains Step by Step

    A detailed walkthrough of the Spring Security filter chain and how requests are processed internally.

  2. How to Log Spring Security Authorization Decisions

    Learn how Spring Security decides allow or deny access, and how to log those decisions clearly.

🐞 Part 4 — Debugging 401 / 403 Errors

  1. Why Spring Security Returns 401 or 403 — and How to Fix It

    A conceptual explanation of authentication vs authorization failures, with real examples.

  2. Debugging Spring Boot Security: Why You Keep Getting 403

    A practical debugging guide when everything looks correct but access is still denied.

  3. Token Is Valid but Still 403 — 5 Real Reasons in Spring Security

    When JWT validation passes but authorization still fails — the most common hidden causes.

  4. Debugging SSO Authentication — Common Issues in Spring Security

    A collection of real-world SSO issues and how to systematically troubleshoot them.

🧭 Recommended Reading Order

  • Start with SSO concepts and protocols
  • Integrate Keycloak and understand WebFlux differences
  • Learn how Spring Security processes requests internally
  • Finish with deep debugging techniques for 401 / 403 issues

🎯 Who This Series Is For

  • Backend developers using Spring Boot or Spring WebFlux
  • Engineers struggling with unexplained 401 / 403 errors
  • Anyone who wants to truly understand Spring Security internals

This series pairs naturally with the Next.js + NextAuth.js Frontend SSO Series , providing a complete frontend + backend SSO reference.

Part of Lengerrong Blog

Comments

Post a Comment

Popular Posts

2026 Begins: Choosing to Stay on the Path as a Blogger

By
Image
  Today is January 1st, 2026 . Before rushing into new goals, I spent some time looking back at the past 12 months of data for this blog — the quiet numbers that tell a very honest story. Looking Back at the Numbers Over the past year: 📈 Total views: ~44,600 👀 Daily average visits: ~200 💬 Comments: 19 💰 AdSense income: about $0.01 per month At first glance, these numbers may look small — especially the income. But when I zoom out, I see something more meaningful. This blog has been quietly read every single day . No viral posts. No aggressive promotion. No paid traffic. Just consistent readers arriving through search, bookmarks, and curiosity. That consistency matters. What the Traffic Graph Tells Me The graph over the last 12 months shows something important: Early months were quiet and uneven Mid-year brought steady growth Toward the end of the year, traffic became more stable , with clear spikes when certain posts resonated This tell...
Read more

Health Checks and Scaling Strategies for Next.js in Kubernetes

By
Image
Health Checks and Scaling Strategies for Next.js in Kubernetes This is Part 6 and the final post of the series: Self-Hosting Next.js in Kubernetes (Without Vercel) . At this point, your Next.js standalone app: Builds cleanly Runs in a minimal Docker image Deploys correctly on Kubernetes / OpenShift Serves static assets properly Uses runtime configuration and secrets Now let’s make it resilient and scalable . Why Health Checks Matter Kubernetes relies on health checks to: Know when a pod is ready to receive traffic Restart unhealthy containers Safely roll out new versions Without proper probes, traffic can be sent to a pod that isn’t ready yet. Readiness Probe A readiness probe tells Kubernetes: “This pod can accept traffic.” For most Next.js apps, the root path works well: readinessProbe: httpGet: path: / port: 3000 initialDelaySeconds: 10 periodSeconds: 5 If your app depends on downstream services (APIs, d...
Read more