The correct answer is 'Authentication' because the implemented access code from a hardware token is an additional authentication factor that must be presented along with the username and password. This is known as multi-factor authentication (MFA), which significantly increases the security by requiring multiple forms of verification before granting access.

The incorrect choices are: 'Authorization' refers to granting or denying rights to a user, resource, or service once authentication has been successful. 'Accounting' involves tracking user activities and resource usage, which could be for billing or auditing purposes. 'Non-repudiation' ensures that a person or entity cannot deny sending a message or transaction, which is not directly enhanced by the addition of a hardware token.