You will run an app on a Windows Compute Engine VM that connects to Cloud SQL via the Cloud SQL Auth Proxy. You created a custom service account and want least-privilege access. What next?

The correct answer ensures least-privilege access by creating a custom IAM role with only the cloudsql.instances.connect permission. This is the minimum permission required for the Cloud SQL Auth Proxy to establish a connection. Starting the proxy with the instance connection name is the standard method for connecting to Cloud SQL. Granting roles/cloudsql.client is a valid option for the Cloud SQL Auth Proxy, but the question specifically asks for least-privilege access, and a custom role with only cloudsql.instances.connect is more restrictive than the predefined cloudsql.client role, which includes additional permissions. The --unix-socket option is typically used for Linux environments, not Windows, and isn't directly related to the IAM permissions. roles/cloudsql.editor grants broad permissions, including modifying Cloud SQL instances, which violates the principle of least privilege for a connection proxy. roles/cloudsql.viewer only allows viewing Cloud SQL instances and does not grant permission to connect, so the proxy would fail.