This is a method used by most modern API-based cloud-computing and storage services, including Amazon Web Services (AWS). In contrast with session-based and token-based approaches, that rely upon a transport layer that can be theoretically accessed by/exposed to a third-party attacker, signature-based authentication performs a hash of the whole request using a previously shared private key. This ensures that no intruder or man-in-the-middle can ever act as the requesting user, as they won't be able to sign the request.