What is the specific technical mechanism used to implement idempotency for a `POST /otp/generate` endpoint to prevent duplicate OTP creation or validation requests?

The specific technical mechanism to implement idempotency for a `POST /otp/generate` endpoint, preventing duplicate OTP creation or validation requests, relies on a unique, client-generated identifier known as an idempotency key. This key ensures that multiple identical requests are treated as a single logical operation, producing the same outcome without unintended side effects.When a client initiates a request to `POST /otp/generate`, it first generates a unique idempotency key, typically a Universally Unique Identifier (UUID), which is a 128-bit number designed to be globally unique. This key is then included in the request headers, commonly within an `Idempotency-Key` header.Upon receiving the request, the server extracts this idempotency key. It then consults a dedicated storage mechanism, such as a distributed cache (like Redis) or a database table, to check if this specific key has been processed before. This storage holds records of idempotency keys along with their associated request status and, if applicable, the response that was previously generated.If the idempotency key is not found in storage, it indicates a new, unique request. The server proceeds with the OTP generation process. Before or during this process, the server stores the idempotency key in its dedicated storage, marking its status as 'in progress' or similar. Once the OTP is successfully generated and persisted (e.g., associated with a user and ready for delivery), the server updates the key's status to 'completed' and stores the complete response body that will be sent back to the client. Finally, the server sends the OTP details as the response to the client.If the idempotency key *isfound in storage, it signifies a duplicate request. The server then checks the stored status associated with that key. If the status is 'completed', the server immediately retrieves the previously stored response associated with that key and returns it to the client. This action occurs without re-executing the OTP generation logic, ensuring that a new OTP is not created. If the status indicates 'in progress', the server might either wait for the initial request to complete and then return its result, or return an appropriate error status like HTTP 409 Conflict, depending on the desired behavior for concurrent duplicates. For OTP generation, returning the original successful response is the primary goal.The server typically responds with an HTTP 200 OK status code for both the initial successful request and subsequent successful idempotent retries, ensuring the client receives a consistent result. To manage storage consumption, idempotency keys and their associated states are usually configured to expire after a defined period (e.g., 24 hours to a few days), after which a new request with the same key would be treated as a fresh operation.