Which of the following is a functionality provided by Okta as an identity-as-a-service (IDaaS)?

The correct choice highlights a key feature of Okta's offerings as an identity-as-a-service (IDaaS) provider—its pre-built application connectors. This functionality allows organizations to easily integrate and manage user identities across a vast array of applications, enhancing the user experience and simplifying access management.

By providing pre-built connectors to thousands of applications, Okta allows companies to streamline user provisioning, single sign-on (SSO), and security policies across different platforms without the need for extensive custom development. This capability is crucial for businesses that rely on multiple software solutions, enabling them to efficiently manage user access and maintain security compliance.

Other options mentioned, such as mobile device authentication services, system-level access to machines, and hosting for custom-built applications, while relevant in different contexts, do not encapsulate the primary functionality expected from an identity-as-a-service provider like Okta. The essence of IDaaS lies in facilitating identity management and access provisioning, which is concretely represented by the extensive library of application connectors.