Part 8 of Building Instagram's Authentication Backend . If you're just joining, the repo is here and you can catch the earlier parts on the YouTube playlist . We built an engine with no ignition Here's where we actually stood after seven parts of this series. We had a fully working AuthService — register, login, refresh, the works. We had a security layer sitting on top of it, filtering every request, deciding who's allowed where. We had entities, repositories, DTOs, a whole exception-handling backbone. And none of it had a URL. Not one line of that code could be reached from outside the JVM. No curl command, no Postman request, nothing. It's a strange feeling to have written that much working logic and still not be able to actually call any of it. So that's what this part is about — wiring up the front door. The controller, and why it's boring on purpose Here's the register endpoint, in full: @PostMapping ( "/registe...
In Episode 2 we poured the foundation — the project, every dependency, and all the configuration in one place. Before we build a single feature on top of it, we build the part that most tutorials skip entirely: error handling . Episode 3 is about making every failure look the same. When something goes wrong in an API — a bad password, a duplicate email, an expired token — the client should get back one predictable shape, with the right HTTP status and a stable error code it can actually program against. No stack traces leaking to users. No endpoint returning 200 OK with an error buried inside. Today we build that backbone: a response envelope, a set of typed exceptions, and one handler that translates all of them. What you’ll learn in Episode 3 This episode is the first real code of the series — and it’s deliberately unglamorous, because a consistent error contract is what makes everything after it pleasant to build. By the end you...
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