Medior/Senior Fullstack Engineer

About the job

We're building critical digital identity and trust infrastructure - PKI, certification services, and identity validation systems that power financial institutions and regulated services. While our backend team handles the core cryptographic engine, we need someone to translate that complexity into performant, secure, usable systems.

This is a fullstack role with backend focus, but the frontend work isn't trivial: you'll be implementing authentication flows, secure session management, and user-facing controls for highly sensitive operations.

What you'll be working on

• Building operational interfaces for certificate lifecycle management, identity validation workflows, and compliance monitoring
• Implementing secure authentication and authorization flows - OAuth2/OIDC, JWT handling, session management in regulated contexts
• Developing performant APIs and integrations that connect frontend interfaces to core infrastructure services and other parties
• Ensuring frontend security - proper token handling, CORS, CSRF protection, XSS prevention in high-stakes environments
• Supporting backend integration work - REST APIs, async processing, background jobs, database optimization 

You'll collaborate closely with:

• Senior backend engineers who handle core PKI/cryptography
• Product managers who navigate regulatory requirements
• A team that's shipped critical, regulated systems before

What we're looking for

Fullstack foundation:

• 3-5+ years developing production systems (medior to senior level)
• Experience in regulated or complex domains (finance, healthcare, identity, government, critical infrastructure)
• Comfortable working across backend and frontend, with stronger backend chops
• Track record of shipping features that actually work in production

Technology flexibility (important for this role)

The project spans multiple technologies and evolving requirements. You don't need to know everything, but you need to adapt quickly and learn independently - you should be able to pick up new tools and patterns on the go.

Backend Stack (need strong experience in at least one):

• .NET
• .NET 6+ / .NET 10 (ASP.NET Core, Web API) 
• C#, async/await, background workers 
• Experience with REST API programming, asynchronous programming, and background processing in .NET 
• Entity Framework Core 
• Experience with multithreading and concurrency 

Java

• Java 11+ / 17+ 
• Spring Boot, Spring Security, Spring Data 
• Experience with multithreading and concurrency 

Databases

• Strong SQL knowledge and schema design skills
• PostgreSQL or MS SQL Server
• Experience with transactions, locking, indexing, and performance tuning 

Frontend:

JavaScript

Experience with at least one modern frontend framework: Angular, React, or Vue.js.

Practical experience with: HTML5, CSS3, responsive layouts, Authentication flows (JWT, OAuth2/OIDC)

Understanding of secure frontend–backend communication, browser security concepts (CORS, CSRF, XSS), and secure handling of user sessions and tokens  

Significant advantages for having some of the following:

DevOps & Infrastructure awareness:

• Docker experience (writing Dockerfiles, running containerized services)
• CI/CD pipelines (GitLab CI, GitHub Actions, Azure DevOps)
• Linux environments and basic system administration
• Configuration management (environment variables, secrets handling)
• Container orchestration concepts (Kubernetes experience is a plus)

Architectural understanding:

• Understanding of OOP, SOLID principles, design patterns
• Experience designing RESTful APIs (OpenAPI/Swagger/Scalar)
• Knowledge of OAuth2, OpenID Connect, JWT, service-to-service authentication
• Experience with long-running background processes, schedulers, and queue-based processing
• Familiarity with distributed systems and multi-instance deployments

Domain knowledge (you'll learn this, but helpful if you have it):

• Regulatory frameworks (eIDAS, ETSI, PSD2, SEPA)
• PKI concepts (certificates, keys, CRL, OCSP)
• Digital signatures (PAdES, XAdES, CAdES)
• HSM integration and secure key storage

What makes this team work

Serious about the work. We're an experienced team that respects the gravity of what we're building while keeping things collaborative and human.

• Compliance is handled: Dedicated PMs manage regulatory navigation and support the requirements management. Everyone collaborates and shares context.
• We've been here before: The team has shipped regulated, critical systems. You won't be explaining why testing matters or why shortcuts aren't acceptable.
• High trust, high accountability: We expect you to own your work, ask for help when needed, and deliver what you commit to.

What we offer:

• Competitive salary with performance-based bonuses
• Private health insurance
• Flexible working hours and a hybrid work model option
• Note: due to the project's nature, we expect the presence in our Belgrade office
• Exposure to advanced security, cryptography, and PKI systems 
• Long-term, stable project with clear technical ownership