Final answer:
Toby is at the authentication stage when asked for a password after providing his username, as this stage involves verifying his identity against the claimed identity.
Step-by-step explanation:
When Toby provides his username at the prompt and is then asked to provide a password, he is in the authentication stage of the access control process. This is because at this stage, the system is attempting to verify the identity that Toby claims to be. Identification usually precedes authentication and involves presenting a username or ID number. After authentication, we typically have authorization, which is the process of determining if the authenticated user has permissions to access certain resources or actions. The option that best fits the described stage is D. Authentication.