Use these credentials to authenticate during the HTTP upgrade request (Basic authorization type, USER:[PASS]).
Passwords specified here will be world-readable in the Nix store! To pass a password to the service, point the
environmentFile option to a file containing HTTP_PASSWORD=<your-password-here> and set this option to <user>:$HTTP_PASSWORD. Note however that this will also locally leak the passwords at runtime via e.g. /proc/<pid>/cmdline.