Information
Rescue mode (former single user mode) is used for recovery when the system detects an issue during boot or by manual selection from the bootloader.
Rationale:
Requiring authentication in rescue mode (former single user mode) prevents an unauthorized user from rebooting the system into rescue mode to gain root privileges without credentials.
Solution
The systemd drop-in files must be created if it is necessary to change the default settings:
Create the file /etc/systemd/system/rescue.service.d/00-require-auth.conf which contains only the configuration to be overridden:
[Service]
ExecStart=-/usr/lib/systemd/systemd-sulogin-shell rescue
Additional Information:
systemd-unit(5)