Sunil — Java / Spring Boot backend developer

Backend systems that don't fall apart under real money and real load.

Fintech and e-commerce systems built to handle concurrency, encrypted data, and failure — not just the happy path.

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About
Portrait of Sunil, backend developer
Backend developer, based in Kathmandu, Nepal

I like backend work because the interesting problems aren't in the endpoint — they're in what happens when two requests hit the same row at once, when a partner's API changes underneath you, or when a queue backs up and nobody notices for an hour. That's mostly what I've spent the last couple of years on: fintech and HR systems handling real transactions and real personal data, where getting it almost right isn't good enough.

I'm currently building FashionMart on my own — a large e-commerce platform where I'm making all the architecture calls myself, for the first time without anyone reviewing the decision before it ships.

If something here looks like the kind of problem you're dealing with, I'd like to hear about it.

Experience

Two years building production backend systems — the featured case studies below cover the work in depth.

Auth & Access ControlFintech / PaymentsEvent-Driven SystemsTesting & Reliability

Java Backend Developer

Rebooted Creation Labs — Kathmandu, Nepal

August 2024 – April 2026

  • Built eKYC with encrypted PII handling and biometric verification for a bank partner integration.
  • Designed a dynamic RBAC and commission engine used platform-wide for merchant onboarding and payouts.
  • Fixed a race condition in wallet balance updates using optimistic locking, eliminating concurrent corruption.
  • Built face-auth + QR attendance check-in/checkout and MFA-secured auth for an HR platform used company-wide.
  • Standardized error handling and wrote JUnit/Mockito coverage across success paths, edge cases, and full API-to-database flows.
Selected WorkCase studies

Five projects, read as engineering problems — not feature lists.

01

Money Transfer & Bank Partner Integration

Confidential fintech platform — Rebooted Creation Labs · Production · Team project

Problem

Domestic money transfer (DMT) requires integrating with multiple bank partners, each with their own onboarding (eKYC) and transaction APIs — while keeping customer data encrypted and processing transaction status that arrives asynchronously.

Ownership

Owned eKYC/onboarding and transaction processing for a bank partner integration, plus multi-provider sender search and commission distribution on the platform’s DMT module.

Method

Built eKYC onboarding with biometric verification and encrypted handling of customer data. Built transaction, balance, and refund endpoints with webhook-driven async status updates. Used Redis for caching and RabbitMQ for decoupled async processing.

Outcome

Shipped production KYC and transaction services for a live bank partner integration, handling real customer data and financial transactions safely.

  • Spring Boot
  • RabbitMQ
  • Redis
  • PostgreSQL
  • Webhooks
02

Merchant Admin & Access Control

Confidential fintech platform — Rebooted Creation Labs · Production · Team project

Problem

A fintech distribution platform needs a secure admin backend to onboard merchants and organizations, enforce role-based access at scale, and calculate commissions correctly.

Ownership

Primary contributor to the platform’s merchant/admin backend module.

Method

Built JWT-based auth with MFA and trusted-device management. Designed a dynamic RBAC system — roles, permissions, and menus generated per user rather than hardcoded. Built a commission engine backed by Redis-cached config and an audit trail for compliance.

Outcome

Became the team’s primary contributor to the platform’s core access-control and payout logic, now underpinning how every merchant is provisioned and paid.

  • Spring Security
  • JWT
  • MFA
  • RBAC
  • Redis
03

HR Management System

Rebooted Creation Labs · Production · Primary contributor

Problem

The company needed an internal HR platform covering secure employee auth, attendance tracking, leave/WFH management, and salary calculation — used company-wide.

Ownership

Primary contributor and owner of the auth, attendance, and role/department management modules.

Method

Built MFA-secured authentication with token rotation. Implemented face-auth and QR-based check-in/checkout with auto-checkout, plus a role/department/position hierarchy. Built leave, WFH, and salary calculation, and an employee onboarding/verification flow.

Outcome

Became the platform’s core attendance and identity system, shipped to production and used company-wide.

  • Spring Boot
  • JWT
  • MFA
  • Face-auth
  • PostgreSQL
04

FashionMart

Ongoing

Personal project · Built and owned from the ground up

Problem

Fashion e-commerce platforms need to handle heavy read/browse traffic, spiky checkout load, and a complex multi-stage order lifecycle (returns, exchanges, trials) without services stepping on each other’s data.

Ownership

Personal project, built and owned from early stages — architecture, service boundaries, and cross-cutting patterns (logging, RBAC, ID exposure) now serve as the reference implementation across the codebase.

Method

Hexagonal/DDD microservices split by domain — product, order, cart, inventory, payment, shipping, analytics, and more. JPA for writes, MyBatis for reads. Kafka with the outbox pattern for reliable cross-service eventing. Redis/Caffeine for caching. GraphQL where flexible querying beats REST rigidity.

Outcome

Found and fixed a critical order_id type mismatch that was silently dropping Kafka order events. Ran a full RBAC security audit, closing under-permissioned endpoints. Refactored logging platform-wide with correlation-ID threading for cross-service traceability.

  • Kafka
  • DDD / Hexagonal
  • JPA + MyBatis
  • GraphQL
  • Redis / Caffeine
05

CareSync

Final-Year Capstone · Solo project · Public GitHub repo

Problem

When multiple family members care for an elderly or physically unable loved one, medication coordination breaks down silently — one caregiver gives a dose, another unaware caregiver gives it again, a real overdose risk.

Ownership

Designed and built solo — full-stack, from problem definition through backend and frontend implementation.

Method

Built a shared caregiving platform where family members coordinate around one patient profile. Core mechanism: a confirmation-based logging system with real-time notifications, duplicate-dose detection, time-window validation, and a full audit trail. JWT-based auth with role-based access control. Patient-facing UI deliberately simplified for elderly users.

Outcome

A working full-stack system that turns a real, dangerous coordination gap in home caregiving into a solvable software problem.

  • React
  • Spring Boot
  • PostgreSQL
  • JWT
Other ProjectsSmaller builds & experiments

  • Bank Partner Mock Server

    Spring Boot

    Simulator for a DMT partner’s API — remitter eKYC, beneficiary management, transaction send/status, and penny-drop verification — for development and testing without a live bank partner.

  • Passkey Authentication

    Spring Boot · WebAuthn · Spring Security

    Passwordless login via WebAuthn/FIDO2 passkeys.

  • Spring Security with JWT Authentication

    Spring Boot · JWT

    Stateless auth with RBAC and secured endpoints.

  • Event-Driven Email Notifications

    Spring Boot · RabbitMQ · Thymeleaf

    Async email delivery via message queues with HTML templates.

  • AWS LocalStack Integration

    Spring Boot · Docker · LocalStack

    Local AWS simulation integrating S3 and SQS for cloud-ready development.

Skills

The stack I reach for.

Core Stack

  • Java
  • Spring Boot
  • Spring MVC
  • Spring Data JPA
  • Spring Security
  • SQL
  • PostgreSQL
  • JWT
  • REST API Design
  • Microservices
  • DDD / Hexagonal Architecture

Also Worked With

  • Kafka
  • RabbitMQ
  • Redis
  • MongoDB
  • MySQL
  • Hibernate
  • Keycloak (SSO/RBAC)
  • WebAuthn / Passkey
  • MFA / OTP
  • GraphQL
  • Docker
  • JUnit
  • Mockito
  • Git
  • Postman