Oleg Z.’s Post

Managing user sessions in microservices can get complex. Instead of storing sessions on the server, JWT (JSON Web Token) makes authentication stateless and scalable by embedding user info and a signature directly into the token. To use JWT effectively:   1. Keep access tokens short-lived (e.g., 30 minutes)   2. Use refresh tokens for longer sessions (e.g., 24 hours)   3. Always store tokens securely on the client side In my application, I’ve configured the access token to expire after 30 minutes and the refresh token after 24 hours. Both are generated using generateAccessToken and generateRefreshToken methods in jwtUtil, and the backend response includes these two tokens for the client to use. In this short video, I break down: JWT structure (Header, Payload, Signature) JWT lifecycle (Login → Token issued → Verified → Access granted) Access vs Refresh tokens with a practical example Best practices for secure, scalable authentication How do you handle JWT expiration and refresh in your projects? #BackendDevelopment #Java #SpringBoot #Microservices #JWT

🚀 Understanding Spring Security with JWT Authentication (Complete Flow) Just built and visualized the complete authentication & authorization flow using Spring Boot + Spring Security + JWT 🔐 📌 Key Highlights from the Architecture: ✔️ Client sends login request → /api/auth/login ✔️ Authentication handled via Authentication Manager ✔️ Credentials verified using DAO Authentication Provider ✔️ User fetched from DB using UserDetailsService ✔️ On success → JWT Token generated (with roles & user info) ✔️ Token sent back to client 🔁 For every next request: ➡️ Client sends JWT in Authorization Header ➡️ JWT Filter validates token ➡️ SecurityContext is set ➡️ Role-based access control using @PreAuthorize ❌ Invalid token → 403 Forbidden ✅ Valid token → 200 OK 💡 This setup ensures: Stateless authentication Secure APIs Role-based access control (ADMIN, USER, etc.) 🔥 Currently working on building a full-stack system around this (like Airbnb-style backend). #SpringBoot #Java #BackendDevelopment #JWT #SpringSecurity #RESTAPI #FullStackDeveloper #LearningInPublic #TechJourney

Understanding JWT( JSON Web Token) Authentication in Spring Boot Most of the time, I was just using JWT in projects without really knowing what was happening behind the scenes. So I spent some time digging into how it actually works. 🔐 What happens during login? * Backend verifies credentials * Generates a JWT token * Sends it to the client After that, the client sends this token with every request instead of credentials. 🧩 The interesting part is Spring Security: Every request passes through a filter chain before reaching the controller. 👉 I implemented a custom JWT filter: * Extract token from header * Validate signature & expiry * If valid → set authentication in Security Context Only then the request is processed. 💡 Took me time to understand this flow — especially tracing how requests move through the filter chain. * JWT = stateless (no session stored on server) * Authentication = who you are * Authorization = what you can access * Everything is decided before controller logic runs 🛠 Still figuring out: * Exact execution point of the filter * Role of SecurityContextHolder * Debugging filter chain flow 📌 Earlier JWT felt like just a library feature. Now it feels like a request validation mechanism at the filter level. Still learning, but this changed how I see backend security. #Java #SpringBoot #SpringSecurity #JWT #BackendDevelopment

🔐 Understanding JWT Authentication in Spring Boot When building secure APIs with Spring Boot, authentication becomes essential. One of the most popular approaches is using JSON Web Tokens (JWT). JWT allows stateless authentication, meaning the server does not need to store session data. Each request carries its own authentication proof inside a token. Efficient, scalable, and perfect for modern REST APIs. Because apparently servers already have enough problems without remembering every user session. Here’s the basic JWT flow in Spring Boot: User logs in with credentials Spring Security authenticates the user A JWT token is generated The token is returned to the client The client sends the token in the Authorization header for future requests Spring validates the token before granting access Why developers use JWT in Spring Boot: Stateless authentication Better scalability Secure API communication Easy integration with frontend frameworks Works well with microservices architecture Typical Spring Boot stack for JWT: Spring Security JWT Library (like JJWT) Authentication Filter UserDetailsService Custom Authentication Provider JWT is not just about login security. It’s about building APIs that remain lightweight, scalable, and maintainable. #SpringBoot #JWT #Java #SpringSecurity #BackendDevelopment #RESTAPI #Programming #SoftwareEngineering #JavaDeveloper

Your API's success isn't just about the "Happy Path." It's about how you handle failure. 🛠️ I still see many Spring Boot projects letting raw StackTraces or generic "500 Internal Server Error" messages leak to the client. This is a security risk and a nightmare for the frontend team. The Senior Way: @RestControllerAdvice Instead of cluttering your business logic with try-catch blocks, use a Global Exception Handler to: ✅ Standardize Responses: Return a consistent JSON structure (Code, Message, Timestamp). ✅ Hide Internals: Map database or business exceptions to user-friendly messages. ✅ Clean Code: Keep your Services focused on the logic, not on error formatting. Pro Tip: Don't just catch Exception.class. Create custom Domain Exceptions (e.g., ResourceNotFoundException) to provide specific HTTP status codes. It makes your API predictable and professional. How do you manage errors in your distributed systems? Do you use a global handler or a different pattern? 👇 #Java #SpringBoot #API #CleanCode #Backend #SoftwareArchitecture #WebDevelopment #Microservices

🔐 Securing Backend APIs like a Pro! Recently, I explored and implemented Spring Security with JWT Authentication to secure my backend APIs. While building my project, I realized that writing APIs is just one part — securing them is what truly makes them production-ready. Here’s what I worked on: ✅ Implemented authentication using JWT (JSON Web Tokens) ✅ Secured REST APIs with Spring Security ✅ Built custom authentication filters ✅ Managed roles and authorities for authorization ✅ Ensured stateless session handling 💡 This experience helped me understand how real-world applications handle user authentication, authorization, and API protection. Now, my backend is not just functional — it’s secure, scalable, and closer to industry standards. 🔗 GitHub Repository: https://lnkd.in/dj-fivea 📘 Learn more about JWT: https://www.jwt.io/ 📌 Next, I’m planning to dive deeper into: • OAuth 2.0 • Role-based access control (RBAC) • Microservices security If you’ve worked with Spring Security or JWT, I’d love to hear your insights! #Java #SpringBoot #SpringSecurity #JWT #BackendDevelopment #WebDevelopment #LearningJourney #SoftwareEngineering

🔐 How JWT Authentication Works (Step-by-Step) This infographic explains the complete flow of JWT (JSON Web Token) authentication in a simple and structured way: 👉 User Login – The user enters credentials (username & password) from the frontend and sends a request to the server. 👉 Credential Verification – The Spring Boot backend validates the user credentials against the database. 👉 JWT Generation – If authentication is successful, the server generates a secure JWT token. 👉 Token Storage – The JWT token is stored in the browser using localStorage or sessionStorage. 👉 API Request with Token – The client sends requests to protected APIs by attaching the token in the header (Authorization: Bearer <token>). 👉 Token Validation – The server verifies the token. If valid, access is granted; otherwise, the request is denied. 💡 Summary JWT helps in building secure, stateless, and scalable authentication systems in modern web applications. As a Java Full Stack learner, understanding this flow is an important step toward real-world backend development 🚀 Still learning and improving every day 💻 #Java #SpringBoot #JWT #Authentication #FullStackDevelopment #BackendDevelopment #WebDevelopment #LearningInPublic #SoftwareEngineering

Understanding HTTP Status Codes Today I focused on an important concept in backend development — HTTP Status Codes While building REST APIs, it’s not just about sending data, but also about sending the right response to the client. 🔹 Learned about different categories of status codes: • 2xx (Success) – 200 OK, 201 Created • 4xx (Client Errors) – 400 Bad Request, 404 Not Found • 5xx (Server Errors) – 500 Internal Server Error 🔹 Understood when to use each status code in real APIs 🔹 Implemented status handling using "ResponseEntity" in Spring Boot This helped me realize how APIs communicate clearly with frontend applications and handle errors properly. Small concept, but very powerful in building real-world applications. Next step: Improving API structure and adding more real-world logic. #Java #SpringBoot #BackendDevelopment #RESTAPI #CodingJourney

🌐 18 Most Common HTTP Status Codes Every Developer Should Know Whether you’re building APIs, working with frontend frameworks, or debugging server responses — understanding HTTP status codes is non‑negotiable. I went through this breakdown, and it’s one of the clearest summaries I’ve seen. If I had something like this earlier, it would’ve saved me a lot of time debugging “mystery errors.” Here’s the quick guide: --- ✅ Success Codes (2xx) These mean your request worked. • 200 OK — Request succeeded • 201 Created — New resource created • 202 Accepted — Request received, processing later • 204 No Content — Success, but no response body --- 🔁 Redirection Codes (3xx) The client needs to take another action. • 301 Moved Permanently — Resource moved forever • 302 Found — Temporary redirect • 304 Not Modified — Use cached version --- ❌ Error Codes (4xx & 5xx) Something went wrong — either client‑side or server‑side. Client Errors (4xx): • 400 Bad Request — Invalid request • 401 Unauthorized — Authentication required • 403 Forbidden — Access denied • 404 Not Found — Resource doesn’t exist • 405 Method Not Allowed — Wrong HTTP method • 408 Request Timeout — Server waited too long Server Errors (5xx): • 500 Internal Server Error — Server failed • 501 Not Implemented — Feature not supported • 502 Bad Gateway — Invalid response from upstream • 503 Service Unavailable — Server overloaded or down • 504 Gateway Timeout — Upstream server didn’t respond --- These are the codes you’ll see every day as a developer. Master them, and debugging becomes 10x faster. #webdevelopment #api #backend #frontend #http #softwareengineering #codingtips #developers

What is a Backend, How it Works, Why We Need It 🚀 I started a deep dive into how backend systems actually work — not just using frameworks, but understanding what happens underneath. Here’s the most powerful insight from today: 👉 A backend is simply a remotely running process that receives requests, does work, and sends back a response. But the real learning was understanding the journey of a request: Browser → DNS → Server (IP) → Firewall → Nginx → Backend → Response And why backend exists in the first place: • To manage data across multiple users • To handle authentication, storage, and business logic • To act as a centralized system (single source of truth) One thing that stood out: Frontend runs in the browser (sandboxed, limited, user-controlled) Backend runs on servers (powerful, secure, scalable) That’s why: ❌ You can’t connect directly to databases from frontend ❌ You can’t bypass CORS easily ❌ You can’t rely on client devices for heavy processing ✔ Backend solves all of this. I’ve compiled detailed notes from the video of K Srinivas Rao into a PDF 👇 This is just Day 1 — more to come. #BackendEngineering #SystemDesign #Java #SpringBoot