Basic authentication configurations for Lighttpd under Ubuntu

lighttpd.conf

apt install apache2-utils
htpasswd -c /etc/lighttpd/.htpasswd <Username> #Replace <Username>, you will be prompted to enter the password.

# Make sure that "mod_auth" is loaded in "server.modules".

nano /etc/lighttpd/lighttpd.conf
#Add the following to lighttpd.conf.

auth.backend = "htpasswd"
auth.backend.htpasswd.userfile= "/etc/lighttpd/.htpasswd"
auth.require = ( "/RestrictedURL" => 
    (
    "method"  => "basic",
    "realm"   => "Restricted!",
    "require" => "valid-user"
    ),
)