sudo chown -R www-data:www-data /var/www/html*
sudo find /var/www/html/ -type d -exec chmod 775 {} \;
sudo find /var/www/html/ -type f -exec chmod 664 {} \;
sudo find /var/www/html -type d -exec chmod g+s {} \;
sudo systemctl restart nginx

Generate Basic Auth Credentials

sudo apt update
sudp apt install htpasswd

htpasswd -n                                       # display the results on standard output rather than updating a file
htpasswd -c ~/public_html/.htpasswd werner        # generate ".htpasswd" file and create credentials for user "werner"
htpasswd ~/public_html/.htpasswd werner           # create or modify credentials for user "werner" in ".htpasswd" file