apt-get install apache2-utils htpasswd -c /etc/apache2/.htpasswd <username>
AuthType Basic AuthName "Restricted Content" AuthUserFile /etc/apache2/.htpasswd Require valid-user
<Directory /var/www/example>
AllowOverride All
Options FollowSymlinks
AuthType Basic
AuthName "Restricted Content"
AuthUserFile /etc/apache2/.htpasswd
Require valid-user
</Directory>
<Location /admin>
AuthUserFile /var/www/htpasswd/.htpasswd
AuthName "Password Protected Area"
AuthType Basic
Require valid-user
</Location>
Do it for both non-ssl and ssl vhost configuration
apachectl -t systemctl reload apache2