Cynthia is concerned about attacks against an application programming interface (API) that her company provides for its customers. What should she recommend to ensure that the API is only used by customers who have paid for the service?
The correct answer and explanation is:
The correct answer is that Cynthia should recommend implementing a robust Authentication and Authorization system for the API.
Explanation:
To ensure that the API is only used by customers who have paid for the service, Cynthia needs to establish a mechanism that verifies the identity of every incoming request and checks if that identity is associated with a currently active, paid account. This is achieved through authentication and authorization.
Authentication is the process of verifying the identity of the caller. Common methods for APIs include:
- API Keys: Unique, secret strings issued to each paid customer. The customer includes this key in each API request (e.g., in a header). The API backend looks up the key to identify the customer.
- Token-Based Authentication (e.g., using OAuth 2.0): Customers’ applications authenticate (perhaps using client credentials) to an authorization server to obtain a temporary access token. This token is included in subsequent API requests. The API validates the token’s signature and expiration.
Authorization is the process of determining what an authenticated caller is allowed to do. In this case, the authorization check is simple: Is the authenticated customer’s account marked as ‘paid’ and ‘active’ in the company’s billing or user management system?
By requiring mandatory authentication on all API endpoints and coupling the validation process with a check against the billing system for paid status, Cynthia can effectively gate access. Requests without valid credentials, or from credentials linked to unpaid/inactive accounts, should be rejected with an appropriate error response (e.g., 401 Unauthorized or 403 Forbidden). This approach prevents unauthorized access, allows for tracking usage per customer, and provides a clear mechanism to revoke access if a customer stops paying. most effective recommendation to ensure that the API is only used by customers who have paid for the service is to implement API Key or Token-Based Authentication and Authorization.
Explanation:
This approach provides a robust method to control access based on a client’s identity and their subscription status. Here’s how it works:
- Authentication: When a customer pays for the service, they are issued a unique, secure API key or access token. This key or token acts as their credential to access the API.
- Inclusion in Requests: Every API request made by the customer must include this key or token, typically in the request headers (e.g., using an Authorization: Bearer <token> header or a custom X-API-Key: <key> header).
- Server-Side Validation: Upon receiving a request, the API backend (or an API Gateway in front of it) validates the provided key or token. This involves looking up the key in a secure database or validating the token’s signature and claims.
- Authorization Check: Crucially, the system linked to the API key/token holds information about the associated customer account, including their current payment or subscription status. Before processing the request, the system checks if the account is active and paid for the service being requested.
- Access Control: If the key/token is valid and the associated account is authorized (i.e., paid), the API request is processed. If the key is invalid, missing, or belongs to an unpaid/inactive account, the request is rejected, usually with an HTTP 401 Unauthorized or 403 Forbidden status code.
This method ensures that only clients presenting valid credentials linked to a paid account can successfully interact with the API, directly addressing Cynthia’s concern about unauthorized usage by non-paying users. Implementing proper key/token lifecycle management, including secure issuance, storage (for API keys), rotation, and prompt revocation upon non-payment or security incidents, is essential for maintaining security.