NGINX Conditional Basic Auth

You can use map block to get an auth_basic directive argument from the $host variable value:

map $host $realm {
    appname.example.com  "Resticted content";
    default              off;
}

server {
    root   /var/www/html/public;
    index index.php;

    auth_basic $realm;
    auth_basic_user_file /var/www/html/public/.htpasswd;

    location / {
        try_files $uri $uri/ /index.php?$args;
    }

    location ~ [^/].php(/|$) {
        ...
    }
}

You can use regex expressions with the map directive using ~ modifier, for example:

map $host $realm {
    ~appname.example.com$  "Resticted content";
    default                  off;
}

Reference: https://stackoverflow.com/a/69538528