Slim V3 - How to block display of credentials on a 404?

Any time I get a “Page Not Found” response from Slim (v3), it lists the Basic Auth credentials in the “Visit the Home Page” link at the bottom of the result. Ugh. That makes me itch.

How do I either block the link/credentials, or modify the 404/PNF output - without having to unset the notFoundHandler?