Middle Python 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.