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Sergio JuntasSJ

Sergio Juntas

Frontend Architect / Tech Lead

€450/day
Madrid, ES
8-15 years

Average response time: 1 hour

Freelancer profile translated to English.
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About Sergio

Frontend Architect / Tech Lead with 10 years of experience building digital products in banking and regulated sectors. Dual specialist in Angular and React/Next.js, with TypeScript as a foundation, I help companies bring critical applications from idea to production: fast, secure, and maintainable.
How I help you:

I lead the frontend of complex platforms where security and scalability are non-negotiable. I design clean architectures (Clean Architecture / Hexagonal) that survive product and team growth, and I integrate enterprise authentication with Azure MSAL and Microsoft Entra ID.
What I have delivered:

• Banking (EVO Banco): Angular funnels for investment and financing products, optimizing the bank's digital sales funnels.

• Logistics (Linde): React CMS architecture for real-time transport control, with role-based management and merchandise traceability.

• Donation platform (dona+): Multi-role React SPA, migration of authentication from Azure MSAL to Microsoft Entra ID, and headless public website with Next.js + Magnolia CMS and high-performance landing pages in Astro.
Types of projects that fit me:

Frontend architecture and leadership, migrations to Angular/React/Next.js, secure applications in regulated environments, authentication with Entra ID, web performance, and SPA platform scaling.
Madrid · Available for remote and on-site projects
  • Spanish

    Native or bilingual

  • English

    Fluent

Can work on-site
Madrid (up to 50km)

Experience

  • INNOCV Solutions
    Frontend Lead - Donation and Parish Management Platform (dona+
    CIVIC AND SOCIAL ORGANIZATIONS
    January 2025 - May 2026 (1 year and 4 months)
    Madrid, Spain
    Led from the Frontend area the integral development of dona+, a digital ecosystem designed to modernize donation collection, optimize parish administration, and automate tax benefits for users.

    Multi-role SPA Architecture (React): Design and development of the main management application in React (consuming ASP.NET services). I structured the platform into two main areas within the same SPA: a global dashboard for administrators and a dedicated portal for parish priests.

    Parish and Tax Management (UX/UI): Implementation of interfaces for parish priests to manage their churches, register new parishes, monitor donations, and execute core functionality: the generation and automated tax relief for tax certificates each fiscal year.

    Security and Authentication: Implementation of the client-side security layer. During the development cycle, I executed the adaptation and migration of the authentication system from Azure MSAL to the new Microsoft Entra ID standard, managing both integrations to ensure a secure and frictionless transition for users.

    Donor Ecosystem (KMP): Coordination of the web platform with the mobile application for end-users (donors), developed in Kotlin Multiplatform (KMP), ensuring a consistent experience throughout the donation cycle.

    Performance and Fundraising (Astro & Next.js): Development of the public web strategy. Initially, I implemented a high-conversion and high-performance landing page in Astro. Later, to scale the project, I led the migration to a headless architecture using Next.js integrated with Magnolia CMS in serverless format, giving full autonomy to the content team.
    React.js Next.js Astro Azure DevOps Docker
  • INNOCV Solutions
    Frontend Lead
    LOGISTICS AND SUPPLY CHAIN
    September 2024 - January 2025 (4 months)
    Madrid, Spain
    Led from the Frontend area the development of the main CMS for Linde's logistics management, a key platform designed to centralize and optimize the control of transports, users, and delivery notes.

    CMS Architecture: Design and development of the web platform (SPA) using React, ensuring seamless integration with the business logic in ASP.NET.

    Management Dashboards and Roles: Building dynamic and secure role-based interfaces for comprehensive management of the transport cycle, from shipment creation to user management and delivery note control.

    Cross-Platform Integration (KMP): Coordinated the coexistence of the CMS with the transporters' application (Kotlin Multiplatform). We replicated the app's functionalities within the web environment itself, allowing drivers to operate seamlessly both from the downloadable mobile app and from the browser.

    Traceability and Visibility (UX): Designed and implemented the views that solved the company's traceability problem. The CMS allows real-time monitoring of the status and location of goods, also integrating the standard barcode reading flow from warehouses.

    Security and Infrastructure: Integration of enterprise authentication using Azure MSAL on the client side, working on a highly scalable and Dockerized deployment environment.
    React.js SignalR Azure DevOps Docker TypeScript
  • INNOCV Solutions
    Senior Frontend Developer - Strategic Projects (EVO Banco)
    BANKING AND INSURANCE
    March 2022 - September 2024 (2 years and 6 months)
    Madrid, Spain
    As the frontend lead for the team, I executed the implementation of high-priority digital products for the institution:

    Conversion Funnels: Developed custom applications with Angular for the acquisition of investment products (deposits) and financing (pre-approved loans), optimizing the bank's digital sales funnels.

    Web Ecosystem: Maintenance and creation of digital assets on OpenCMS, using Vanilla JS and solid CSS architecture to ensure minimal loading times on the corporate website.

    Senior Integration: Worked closely with backend and product areas to translate banking business requirements into functional, robust, and secure interfaces.
    Angular TypeScript RxJS Test driven development Redux

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Education

  • Productivity Tricks for Programmers Certificate of completion
    Claude Platform 101
    Trucos de productividad para programadores Certificate of completion
  • Certificate of completion
    Claude 101
    Certificate of completion

Skill set

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