Add support to your plugin or theme for WordPress Personal Data Exporter (GDPR Compliancy).

plugin-privacy-user-data-exporter.php

<?php

/**
 * Register exporter for Plugin user data.
 *
 * @see https://github.com/allendav/wp-privacy-requests/blob/master/EXPORT.md
 *
 * @param $exporters
 *
 * @return array
 */
function plugin_register_exporters( $exporters ) {
	$exporters[] = array(
		'exporter_friendly_name' => __( 'User Social Accounts' ),
		'callback'               => 'plugin_user_data_exporter',
	);

	return $exporters;
}

add_filter( 'wp_privacy_personal_data_exporters', 'plugin_register_exporters' );

/**
 * Exporter for Plugin user data.
 *
 * @see https://github.com/allendav/wp-privacy-requests/blob/master/EXPORT.md
 *
 * @param     $email_address
 * @param int $page
 *
 * @return array
 */
function plugin_user_data_exporter( $email_address, $page = 1 ) {
	$export_items = array();

	$user = get_user_by( 'email', $email_address );

	if ( $user && $user->ID ) {
		// Most item IDs should look like postType-postID
		// If you don't have a post, comment or other ID to work with,
		// use a unique value to avoid having this item's export
		// combined in the final report with other items of the same id
		$item_id = "user-social-{$user->ID}";

		// Core group IDs include 'comments', 'posts', etc.
		// But you can add your own group IDs as needed
		$group_id = 'user-social';

		// Optional group label. Core provides these for core groups.
		// If you define your own group, the first exporter to
		// include a label will be used as the group label in the
		// final exported report
		$group_label = __( 'User Social Data' );

		// Plugins can add as many items in the item data array as they want
		$data = array();

		// Add the users facebook url
		$facebook_url = get_user_meta( $user->ID, 'facebook_url' );
		if ( $facebook_url ) {
			$data[] = array(
				'name'  => __( 'Facebook URL', 'popup-maker' ),
				'value' => $facebook_url,
			);
		}

		// Add their twitter handle
		$twitter_handle = get_user_meta( $user->ID, 'twitter_handle' );
		if ( $twitter_handle ) {
			$data[] = array(
				'name'  => __( 'Twitter Handle', 'popup-maker' ),
				'value' => $twitter_handle,
			);
		}

		// Add this group of items to the exporters data array.
		$export_items[] = array(
			'group_id'    => $group_id,
			'group_label' => $group_label,
			'item_id'     => $item_id,
			'data'        => $data,
		);

	}

	// Returns an array of exported items for this pass, but also a boolean whether this exporter is finished.
	//If not it will be called again with $page increased by 1.
	return array(
		'data' => $export_items,
		'done' => true,
	);
}