The correct approach is A because service accounts allow applications to securely authenticate and interact with Google Cloud APIs. According to GCP documentation, for applications running outside of GCP (like on-premises), a service account's identity must be established using a public/private key pair. This key pair is generated and downloaded upon creation, with the private key needing secure storage and accessibility for the application to make authenticated API calls. Options B and C are incorrect as default service accounts lack the necessary permissions and are not available for on-premises deployments. Option D, while functional, violates the principle of least privilege by granting editor-level permissions unnecessarily and still requires a key for on-premises use.