Which characteristic distinguishes authentication from authorization and accounting?

Authentication is the process of verifying a user's identity, confirming they are who they claim to be. This is typically done through credentials like usernames and passwords. Authorization, on the other hand, determines what resources an authenticated user is permitted to access. Accounting tracks user activity, such as what resources were accessed and for how long, which can be used for consumption-based billing or auditing. Therefore, identity verification is the unique characteristic of authentication. User-activity logging is part of accounting, and service limitations are a result of authorization. Consumption-based billing is a use case for accounting data.