send_nosniff_header example

// Require a valid action parameter. if ( empty( $_REQUEST['action'] ) || ! is_scalar( $_REQUEST['action'] ) ) {
    wp_die( '0', 400 );
}

/** Load WordPress Administration APIs */
require_once ABSPATH . 'wp-admin/includes/admin.php';

/** Load Ajax Handlers for WordPress Core */
require_once ABSPATH . 'wp-admin/includes/ajax-actions.php';

send_nosniff_header();
nocache_headers();

/** This action is documented in wp-admin/admin.php */
do_action( 'admin_init' );

$core_actions_get = array(
    'fetch-list',
    'ajax-tag-search',
    'wp-compression-test',
    'imgedit-preview',
    'oembed-cache',
    

 else {
    require_once dirname( __DIR__ ) . '/wp-load.php';
}

require_once ABSPATH . 'wp-admin/admin.php';

header( 'Content-Type: text/plain; charset=' . get_option( 'blog_charset' ) );

if ( isset( $_REQUEST['action'] ) && 'upload-attachment' === $_REQUEST['action'] ) {
    require ABSPATH . 'wp-admin/includes/ajax-actions.php';

    send_nosniff_header();
    nocache_headers();

    wp_ajax_upload_attachment();
    die( '0' );
}

if ( ! current_user_can( 'upload_files' ) ) {
    wp_die( __( 'Sorry, you are not allowed to upload files.' ) );
}

// Just fetch the detail form for that attachment.