Configuring Nginx for basic authentication

To configure Nginx for basic authentication, you need to create a file for user and password, update Nginx configurations, and restart Nginx.

Create an user-password file for Nginx.
```
htpasswd -c /etc/nginx/.htpasswd admin
```
This requires the Apache HTTP package to be installed on the system.

Update your Nginx configuration (/etc/nginx/nginx.conf or a custom configuration file in the /etc/nginx/conf.d directory) with the highlighted part:

    server {
        listen              9443 ssl;
        server_name         _;
        ssl_certificate     /<PATH TO CERTIFICATE>/nginx-server-crt.pem;
        ssl_certificate_key /<PATH TO CERTIFICATE>/nginx-server-key.pem;

        location /prometheus/ {
            auth_basic           "Prometheus";
            auth_basic_user_file /etc/nginx/.htpasswd;
            proxy_pass http://localhost:9090/;
        }
    }

Restart Nginx.