A security engineer enhances MFA access with a key card and fingerprint scan. What would add another factor of authentication?

Adding another factor of authentication typically involves incorporating a method that is distinct from the ones already employed in the authentication process. In this scenario, the security engineer is using a key card (something you have) and a fingerprint scan (something you are), which represent two different categories of authentication factors.

By introducing a retina scan, it adds an additional biometric authentication factor, utilizing something you are as well. This not only enhances security by requiring a unique physical trait but also aligns with the principle of multi-factor authentication, where the goal is to require multiple, independent credentials to verify a user's identity.

In contrast, the other options do not effectively add a new category of authentication. A hard token would also be categorized as something you have, while a keypad PIN would be considered something you know. Similarly, an SMS text can be seen as something you have, but doesn't significantly enhance security compared to the existing factors. Therefore, the retina scan stands out as the most effective choice to introduce as an additional factor.