Senior Backend & Smart Contract Engineer
Production-grade Web3 systems · Java/Spring · TypeScript/Node.js · Solidity/EVM

Valencia, Spain · Open to remote opportunities across EMEA and international teams

I build backend services, smart contracts, blockchain integrations, and workflow systems where roles, permissions, money, state, deadlines, and reliability matter.

My background spans more than 15 years of engineering, from industrial automation and operational systems to backend, full-stack, and blockchain development. I bring the same mindset to software that production environments demand: explicit state, controlled failure modes, observable operations, strong testing, and designs that remain understandable under pressure.

My current focus is the intersection of:

• Backend and identity systems — APIs, authentication, federation, persistence, integrations, and CI/CD
• Smart contracts and protocol logic — permissions, state machines, incentives, deadlines, escrow, and payment rules
• Programmable payments — agent spending policies, payment intents, wallets, receipts, and authorization boundaries
• Real-world workflows — aviation, travel, marketplaces, team finance, identity, and operational automation

Policy-controlled HTTP 402 payments for autonomous AI agents.

An agentic-payment system where an autonomous agent can purchase a protected API response only when a deterministic spending policy authorizes it. Payments are bound to exact requests and protected through merchant allowlists, spending limits, expiration checks, audit events, and replay prevention.

The project includes a TypeScript monorepo, protected API, policy engine, agent runner, dashboard, Casper adapter, and an Odra smart contract for recording proof data on Casper Testnet.

Demonstrates: agentic commerce · HTTP 402 · policy engines · request-bound receipts · replay protection · Casper Testnet · on-chain proof recording

Stack: TypeScript · Node.js · Next.js · Rust · Odra · Casper · Vitest

Live demo · Source code · DoraHacks submission

A self-custodial treasury for football teams, squads, and fan groups.

CupTreasury replaces contribution reminders and expense approvals managed through WhatsApp with a structured treasury workflow. Captain and Treasurer approvals are transformed into exact, one-time payment capabilities that can be evaluated through Tether WDK policies.

The project includes contribution tracking, match-day expense requests, role-based approvals, PaymentIntent authorization, WDK policy simulation, safe no-broadcast signing, proof artifacts, automated tests, and a judge-facing verification flow.

Demonstrates: programmable payments · self-custody · approval policies · capability-based authorization · Tether WDK · security boundaries

Stack: Next.js · TypeScript · Tether WDK · React · Vitest · GitHub Actions

Live demo · Source code

Winner of the Blockchain-based Turnaround Checklist challenge at Decode Travel Barcelona 2025.

A smart-contract-backed aviation workflow created with Camino Network and Vueling. Each aircraft turnaround is modeled through task ownership, role permissions, completion states, operational deadlines, SLA and KPI computation, certification, and ERC-721 reward badges.

The project translates a real multi-actor operational process into explicit, auditable smart-contract state transitions.

Demonstrates: operational workflow modeling · smart-contract state machines · deadlines · KPIs · certification · tokenized incentives

Stack: Solidity · TypeScript · Next.js · Camino Network · IPFS · ERC-721

Case study · Source code

A Ganache-like local development environment for Casper applications.

Fondant packages Casper CCTL functionality into a Docker-based application suite with interfaces for accounts, blocks, deploys, events, logs, and local RPC workflows.

It was designed to shorten the feedback loop for developers building and testing Casper smart contracts without relying entirely on shared networks.

Demonstrates: blockchain developer tooling · local infrastructure · Dockerized environments · RPC integration · developer experience

Stack: TypeScript · Rust · Docker · Docker Compose · CCTL · Casper

Case study · Source code

Alongside my public Web3 work, I build backend and identity systems using Java, Spring Boot, PostgreSQL, Keycloak, REST APIs, OpenAPI, Docker, Gradle, and CI/CD.

My professional work includes:

• Identity federation, SSO, authentication flows, and role synchronization
• Keycloak extensions, authenticators, event listeners, and client policies
• REST and gRPC service design
• Database modeling and Flyway migrations
• External provider and blockchain integrations
• Authorization and account lifecycle rules
• Automated unit and integration testing
• Production debugging, system upgrades, and deployment workflows

• Start with the actors, rules, constraints, and failure modes—not the framework.
• Keep contract and API state transitions explicit and testable.
• Treat authentication, wallets, signatures, providers, and external data as reliability boundaries.
• Separate demonstrable functionality from assumptions, simulations, and future production work.
• Use blockchain where it provides verifiable state, traceability, programmable authorization, or meaningful automation.
• Document architecture, trade-offs, trust assumptions, limitations, and production-hardening requirements.

• Autonomous-agent payments and HTTP 402 workflows
• Policy-controlled wallets and programmable payment authorization
• On-chain proof and audit systems
• Blockchain-backed operational workflows
• Backend and identity infrastructure for Web3 products

I am open to remote opportunities involving senior backend engineering, smart contracts, blockchain platforms, Web3 infrastructure, programmable payments, and technically ambitious product development.

Portfolio · LinkedIn · Contact