Implement Unofficial API Integration

I need assistance with integrating a third-party API, for which no documentation is available. You will need to learn how the API works and implement it for us. Once done, we will create our own unofficial API and use that for our backend.

Requirements:
- Learn and understand the API functionalities (data retrieval, submission, and user authentication)
- Implement the API integration
- Collaborate on creating an unofficial API for backend use

Ideal Skills:
- Experience with API integration (REST, SOAP, GraphQL)
- Strong problem-solving skills
- Ability to work without documentation
- Familiarity with backend development