How should the level of detail and focus in client-facing documentation differ when explaining OTP API design rationale to a solution architect compared to providing implementation specifics for a backend developer?

The level of detail and focus in client-facing documentation for an OTP API must fundamentally differ based on the audience, specifically a solution architect versus a backend developer, due to their distinct roles and responsibilities within a project.

For a solution architect, the documentation should focus on the design rationale of the OTP API, which refers to the underlying reasoning, principles, and trade-offs that led to specific architectural and functional choices. This level of detail is high-level and conceptual, explaining *whycertain decisions were made and their impact on the broader system. A solution architect needs to understand the architectural implications, scalability considerations, and security posture of the OTP API within the entire enterprise ecosystem. For instance, the documentation should explain the choice of using a stateless API for OTP generation and verification to ensure horizontal scalability, detailing how the server does not store session information between requests. It should cover the rationale behind specific rate-limiting strategies implemented at the API gateway level to prevent brute-force attacks, explaining the security benefits and potential performance trade-offs. The architect also needs to understand the integration points with existing systems, such as how the OTP API interacts with the user management system for enrollment or with a notification service for delivering OTPs via SMS or email. The documentation should outline the high-level error handling strategy, for example, distinguishing between client-side errors (like invalid input) and server-side errors (like service unavailability), to ensure robust system design. It should also discuss the chosen cryptographic primitives for OTP generation, such as using HMAC-based One-Time Passwords (HOTP) or Time-based One-Time Passwords (TOTP), and the security advantages of that choice, rather than the specific code implementation of those algorithms. The focus remains on strategic alignment, risk mitigation, and overall system coherence.

Conversely, for a backend developer, the documentation must provide implementation specifics, which are the precise details and instructions required to build, configure, and integrate the system component. This level of detail is granular and prescriptive, focusing on *howto interact with and utilize the OTP API. A backend developer requires concrete, actionable information to write code and debug issues. The documentation should detail every API endpoint, such as `/api/otp/generate` and `/api/otp/verify`, including their HTTP methods (e.g., POST) and the exact request and response payloads, specifying data types, required fields, and example values. For example, it would show a JSON request body for OTP generation containing `userId` and `channel` (e.g., 'SMS'), and the corresponding JSON response including a `transactionId`. It must clearly define all possible HTTP status codes and specific error codes (e.g., 400 Bad Request with an error code like `OTP_INVALID_FORMAT`, 401 Unauthorized, 403 Forbidden, 429 Too Many Requests) with their corresponding human-readable messages, enabling the developer to implement robust error handling in their client application. It should specify the authentication and authorization mechanisms required to access the API, such as expecting a JWT in the `Authorization` header and detailing the required scopes or roles. Any specific headers for rate-limiting, like `X-RateLimit-Remaining` or `Retry-After`, must be documented. If idempotency is crucial, the documentation should explain how to achieve it, perhaps by requiring an `Idempotency-Key` header with a unique request identifier, and describe how the API handles duplicate requests based on this key to prevent unintended side effects like generating multiple OTPs for the same transaction. It might include conceptual code snippets showing how to make an API call and parse the response, emphasizing practical usage over architectural philosophy.