Automation of work with the State Tax Service: electronic digital signature, tax reconciliation, and receipt of incoming correspondence

(the project is in the stage of finalization and testing)
Development of a server module for the system (Python/FastAPI, PostgreSQL, Jinja2 UI), which provides automated interaction with the Electronic Cabinet of the State Tax Service through certified cryptographic libraries of JSC "IIT" (EUSignCP). The module should operate in the context of the existing client base of individual entrepreneurs and their tax data.

Functional blocks:

1. Digital Signature Module (EUSign)

   • Integration of the EUSignCP library (server side) for signing and verifying digital signatures.
   • Authorization in the private part of the Electronic Cabinet of the State Tax Service on behalf of individual entrepreneur clients registered in the system.
   • Storage of digital signature key parameters in the existing table (or extension of the model).
   • API endpoints in FastAPI Router format, compatible with the current router architecture.

2. Automatic reconciliation with the budget

   • Programmatic retrieval of data on the status of settlements (accrued, paid, arrears, penalties) from the State Tax Service cabinet for the list of individual entrepreneur clients.
   • Saving results in a new related PostgreSQL table.
   • Integration with the existing TAX module: automatic updating of payment and penalty fields.
   • UI display in the TAX tab via Jinja2 template, aligned with the current design (Bootstrap 5, cards, tables).

3. Receiving incoming documentation

   • Monitoring and automatic downloading of incoming letters, messages, and acts from the State Tax Service from the Electronic Cabinet.
   • Storing documents in the database (new table dps_incoming_documents with fields).
   • Automatic notification (flag for new documents in the client UI interface).
   • Background task (celery/asyncio worker) for periodic checking of new documents.

4. Reporting

   • Generating tax declarations in XML format (Unified Tax, 4DF, Unified Social Contribution) based on data from existing tables.
   • Signing with a digital signature via EUSignCP and sending to the State Tax Service gateway.
   • Monitoring the receipt of receipts No. 1 and No. 2, automatic status updating.
   • Support for report types: Unified Tax, 4DF, Unified Social Contribution, Individual Entrepreneur (according to the field in the model).

5. Integration API layer

   • All endpoints — FastAPI Router with the prefix /api/dps/.
   • Authorization through the existing system (or API keys).
   • Response format — JSON, compatible with current APIs.
   • Documentation via OpenAPI/Swagger (automatic in FastAPI).

Technical requirements for implementation:

• Language/framework: Python 3.11, FastAPI, SQLAlchemy ORM, Pydantic.
• Database: PostgreSQL (Neon-backed), migrations via SQLAlchemy
• Code structure: New router routers/dps.py (or several: routers/dps_eusign.py, routers/dps_docs.py, routers/dps_reports.py). Models added to the existing models.py.
• UI: Jinja2 templates in templates/ui/, included via {% include %} in client_detail.html, styled with Bootstrap 5.
• Queues: Use of asyncio tasks or Celery for bulk processing of requests without blocking.
• Cryptography: Server library EUSignCP (IIT), support for file and hardware keys.

Requirements for the performer:

• Experience with EUSignCP (IIT) cryptography libraries and exchange protocols with the State Tax Service.
• Understanding the structure of tax XML files and transport protocols of gateways.
• Experience in development with Python (FastAPI), SQLAlchemy ORM.
• Ability to work with request queues for bulk processing without blocking.
• Willingness to adhere to existing project code conventions (router, model, template structure).