Backend Engineer

We are looking for a Strong Middle / Senior Python Engineer for a 3-month contract, with a possible extension, to build a verifiable proof module for a humanitarian transparency platform. You will deliver a self-contained backend module that turns delivery attestations into immutable, signed data bundles and reliably exchanges them with an external anchoring service.


🧙‍♂️In This Role You Will

• Build a standalone Django app behind a feature flag, with its own models, migrations, Celery tasks, and routes.
• Implement idempotent, transactional review workflows (verify / withhold / reject / amend) with strict data validation.
• Produce canonical, hashed, and signed data bundles (JSON canonicalization, SHA-256) that conform byte-exactly to agreed test vectors.
• Design reliable outbound delivery using a transactional outbox, Celery workers/beat, retries, and replay.
• Implement signed webhooks (HMAC-SHA256, Standard Webhooks) and runtime secret rotation without redeployment.
• Build machine-to-machine APIs for bundle retrieval, anchor write-back, and public key publication.
• Migrate free-text location data to the official administrative territorial registry (KATOTTG) with versioning.
• Set up a staging harness with synthetic fixtures and run end-to-end dry runs with the integration partner.
• Cover the module with tests, contract conformance checks, and security hardening, and document your work.
  
   

🎯 You May Be Interested If

• You like well-scoped, high-impact work with a clear deadline and a production release at the end.
• You care about correctness, data integrity, and security, not just "it works".
• You're comfortable working autonomously and communicating clearly with an external integration partner.
• You enjoy a small, remote, supportive team.
  
   

🍰 Role Requirements

• 3+ years of backend development with Python and Django.
• Hands-on experience with Celery (workers, beat, retries) and asynchronous/background processing.
• Solid understanding of idempotency, database transactions, and reliable delivery patterns (e.g. transactional outbox).
• Experience designing REST APIs and machine-to-machine integrations, including webhooks and request signing (HMAC).
• Practical knowledge of applied cryptography basics: hashing, digital signatures, secrets and key rotation.
• Strong PostgreSQL skills, including schema design and data migrations.
• Docker-based development, Git, and basic Bash.
• Experience with a cloud platform (Azure, AWS, or GCP).
• English at B1 or higher.
   

Nice to have:

• Familiarity with RFC 8785 (JSON Canonicalization Scheme) or the Standard Webhooks specification.
• Experience with administrative/geographic code registries (e.g. KATOTTG, ISO 3166-2).
• Experience with secret stores / key management services (e.g. Azure Key Vault, AWS KMS, HashiCorp Vault).
  
   

💻 Working Conditions

• Contract: 3 months, full-time load, with possible extension.
• This is a fully remote position with the entire team across Ukraine.
• Flexible working hours; the team agrees deadlines together, with a focus on delivering commitments on time.