An identity architect is setting up an integration between Salesforce and a third-party system.

For a server-to-server integration that should avoid end-user interaction and maximize security, the JWT Bearer Flow is the strongest fit. Salesforce documents it for noninteractive scenarios where a trusted external service can sign an assertion with a certificate and exchange it for an access token. That means no browser- based approval screen, no password collection, and no dependence on a human being present to authorize the session. Web Server and User-Agent flows are designed for interactive delegated access, while username-password is a special-case pattern with weaker security characteristics. The architectural takeaway is simple: when the client is a trusted server and the goal is high assurance with minimal user involvement, certificate-based JWT exchange is the preferred Salesforce approach. This is why option A is the best answer in Salesforce terms.