I will provide a rough, text-based description of a REST API, including endpoints, data models, and authentication methods. Convert this unstructured information into a strictly valid, formatted OpenAPI 3.0 (Swagger) YAML specification. Ensure you correctly define paths, verbs (GET, POST, etc.), request bodies, response codes (including error handling 4xx/5xx), schemas, and security schemes. Do not include explanatory text; output only the raw YAML code.