Senior Go Developer - Integration

CryptoNext Security SAS; Paris; Hybrid; EUR 85,000 - 120,000; Full time

Job summary

CryptoNext Security SAS in Paris seeks a backend engineer to build Go-based connectors for our platform, integrating with client tools, and to design robust API contracts. You will handle asynchronous processing, leverage PostgreSQL and Redis, and containerize deployments.

Join a small team in a hybrid Paris-based setup, collaborating with Product and QA to ship reliable software. You will work with AI-assisted development, maintain observability, and participate in architectural decisions while

Qualifications

• Production Go experience with concurrency and error handling.
• Experience with hexagonal architecture or equivalent design.
• Strong experience with third-party API integration (HTTP, retries, backoff).
• Proficiency in PostgreSQL and Redis usage.
• Familiarity with OpenAPI and REST API versioning.
• Experience writing unit/integration tests and CI/CD pipelines.
• Experience in a startup or deeptech environment.

Responsibilities

• Build and maintain Go connectors linking CryptoNext Platform to client tools.
• Consume heterogeneous APIs with pagination, rate limits, retries, and outages.
• Design and evolve API contracts (OpenAPI) and versioning.
• Model/query PostgreSQL, use Redis, and process async with RabbitMQ.
• Containerize with Docker and Docker Compose; push changes via GitLab CI.
• Instrument services with logs, metrics, traces; diagnose incidents.
• Write tests and review code; onboard new teammates.

Skills

Go concurrency

Hexagonal architecture

HTTP retries

PostgreSQL

Redis

OpenAPI

Testing

CI/CD

AI tools

Tools

Docker

GitLab CI

OpenAPI

Job description

Who we are

CryptoNext Security is a deeptech startup specializing in post-quantum cryptography. Our solutions help businesses and institutions prepare for a future where quantum computers will challenge traditional data security. We work with leading clients in finance, defense, and telecommunications.

On a daily basis, you will

• Build and maintain, in Go, the connectors that link CryptoNext Platform to our clients' tools (CLM, CMDB…): extracting, normalizing and exposing data through REST APIs.
• Consume heterogeneous third-party APIs: handle pagination, rate limits, retries, idempotency and provider outages.
• Design and evolve the API contracts exposed to CryptoNext Platform: OpenAPI and versioning.
• Model and query PostgreSQL, use Redis, and process work asynchronously through RabbitMQ.
• Containerize your deliverables (Dockerfile, Docker Compose) and get your changes through GitLab CI.
• Instrument your services (logs, metrics, traces), diagnose incidents in staging and production, and contribute to root cause analyses.
• Write the unit and integration tests that back your features, including against test doubles of provider APIs, and give QA what they need to automate the rest.
• Review code and help onboard new team members.
• Work directly with Product and QA.
• Use AI coding tools as leverage under your own judgement, staying accountable for what lands in the repo.
• Propose architecture changes and refactorings, and explain the trade-offs you accepted.

How we work

A team of six engineers, within our 15-person R&D department. Connectors live in a monorepo and follow a hexagonal architecture. Three days a week in our Paris office, the rest remote. Short feedback loops, high standards. We ship a working version early rather than polishing in isolation, and keep solutions as simple as the problem allows.

The skills you'll need

• Production Go: concurrency (goroutines, channels), context, explicit error handling, interfaces, modules and standard tooling (go test, go vet).
• Hexagonal architecture (ports and adapters), or the ability to defend an equivalent split.
• Third-party API integration: robust HTTP clients, timeouts, retries with backoff, pagination, rate limiting, idempotency.
• Asynchronous processing: RabbitMQ consumers, acknowledgements, retries and failure handling, dead-lettering, backpressure.
• PostgreSQL: schema design, migrations and rollbacks, indexing, reading a query plan. Hands-on use of Redis.
• API contract design: REST, OpenAPI, versioning.
• Unit and integration testing, with a defensible position on what belongs at which level and on what is worth testing at all.
• Delivery: Docker and Docker Compose, GitLab CI.
• Operations: observability and incident diagnosis.
• Real use of AI-assisted development in a production codebase: agentic workflows, context management, reviewing generated output as critically as a colleague's merge request. You have a view on where these tools pay off and where they create debt.
• Experience means you can say why you chose an approach, what you rejected, and what it will cost in six months.

Bonus skills

• Java.
• Knowledge of the CLM/PKI (X.509 model) and CMDB domains.
• Knowledge and hands-on handling of provider authentication schemes: OAuth2, mTLS, API keys.
• Secure coding practices and application security.
• Experience in a startup or deeptech environment.

The team you'll be joining

You will join a team of six engineers who own their features across the whole stack, inside our 15-person R&D department, working closely with Product and QA. You will report to the Head of Engineering and collaborate with other departments to build the backend services and interfaces our clients depend on.

Our recruitment process

Initial discussion with our HR team to explore your background and motivations.

Technical interview with a developer: a live coding session of 1 to 1.5 hours. AI coding tools are required, not merely allowed. We are interested in how you direct and review them. No take-home assignment.

Meeting with a manager to ensure alignment with our company culture.

If successful, you will receive a final offer!

What's in it for you at CryptoNext

• A stimulating work environment with cutting-edge technological challenges.
• A competitive salary, aligned with our compensation philosophy.
• A deep dive into the exciting world of post-quantum cryptography and cybersecurity.