Information
Single user mode (rescue mode) is used for recovery when the system detects an issue during boot or by manual selection from the bootloader.
Rationale:
Requiring authentication in single user mode (rescue mode) prevents an unauthorized user from rebooting the system into single user to gain root privileges without credentials.
Solution
Edit /usr/lib/systemd/system/rescue.service and add/modify the following line:
ExecStart=-/usr/lib/systemd/systemd-sulogin-shell rescue
Edit /usr/lib/systemd/system/emergency.service and add/modify the following line:
ExecStart=-/usr/lib/systemd/systemd-sulogin-shell emergency