403 Forbidden

<?php

new WPCOM_JSON_API_List_Users_Endpoint( array(
	'description' => 'List the users of a site.',
	'group'       => 'users',
	'stat'        => 'users:list',

	'method'      => 'GET',
	'path'        => '/sites/%s/users',
	'path_labels' => array(
		'$site' => '(int|string) Site ID or domain',
	),

	'query_parameters' => array(
		'number'   => '(int=20) Limit the total number of authors returned.',
		'offset'   => '(int=0) The first n authors to be skipped in the returned array.',
		'order'    => array(
			'DESC' => 'Return authors in descending order.',
			'ASC'  => 'Return authors in ascending order.',
		),
		'order_by' => array(
			'ID'            => 'Order by ID (default).',
			'login'         => 'Order by username.',
			'nicename'      => "Order by nicename.",
			'email'         => 'Order by author email address.',
			'url'           => 'Order by author URL.',
			'registered'    => 'Order by registered date.',
			'display_name'  => 'Order by display name.',
			'post_count'    => 'Order by number of posts published.',
		),
		'authors_only'      => '(bool) Set to true to fetch authors only',
		'type'              => "(string) Specify the post type to query authors for. Only works when combined with the `authors_only` flag. Defaults to 'post'. Post types besides post and page need to be whitelisted using the <code>rest_api_allowed_post_types</code> filter.",
		'search'            => '(string) Find matching users.',
		'search_columns'    => "(array) Specify which columns to check for matching users. Can be any of 'ID', 'user_login', 'user_email', 'user_url', 'user_nicename', and 'display_name'. Only works when combined with `search` parameter.",
		'role'              => '(string) Specify a specific user role to fetch.'
	),

	'response_format' => array(
		'found'    => '(int) The total number of authors found that match the request (ignoring limits and offsets).',
		'authors'  => '(array:author) Array of author objects.',
	),

	'example_response' => '{
		"found": 1,
		"users": [
			{
				"ID": 78972699,
				"login": "apiexamples",
				"email": "justin+apiexamples@a8c.com",
				"name": "apiexamples",
				"first_name": "",
				"last_name": "",
				"nice_name": "apiexamples",
				"URL": "http://apiexamples.wordpress.com",
				"avatar_URL": "https://1.gravatar.com/avatar/a2afb7b6c0e23e5d363d8612fb1bd5ad?s=96&d=identicon&r=G",
				"profile_URL": "https://en.gravatar.com/apiexamples",
				"site_ID": 82974409,
				"roles": [
					"administrator"
				],
				"is_super_admin": false
			}
		]
	}',

	'example_request'      => 'https://public-api.wordpress.com/rest/v1/sites/82974409/users',
	'example_request_data' => array(
		'headers' => array(
			'authorization' => 'Bearer YOUR_API_TOKEN'
		),
	)
) );

class WPCOM_JSON_API_List_Users_Endpoint extends WPCOM_JSON_API_Endpoint {

	var $response_format = array(
		'found'    => '(int) The total number of authors found that match the request (ignoring limits and offsets).',
		'users'  => '(array:author) Array of user objects',
	);

	// /sites/%s/users/ -> $blog_id
	function callback( $path = '', $blog_id = 0 ) {
		$blog_id = $this->api->switch_to_blog_and_validate_user( $this->api->get_blog_id( $blog_id ) );
		if ( is_wp_error( $blog_id ) ) {
			return $blog_id;
		}

		$args = $this->query_args();

		$authors_only = ( ! empty( $args['authors_only'] ) );

		if ( $args['number'] < 1 ) {
			$args['number'] = 20;
		} elseif ( 1000 < $args['number'] ) {
			return new WP_Error( 'invalid_number',  'The NUMBER parameter must be less than or equal to 1000.', 400 );
		}

		if ( $authors_only ) {
			if ( empty( $args['type'] ) ) {
				$args['type'] = 'post';
			}

			if ( ! $this->is_post_type_allowed( $args['type'] ) ) {
				return new WP_Error( 'unknown_post_type', 'Unknown post type', 404 );
			}

			$post_type_object = get_post_type_object( $args['type'] );
			if ( ! $post_type_object || ! current_user_can( $post_type_object->cap->edit_others_posts ) ) {
				return new WP_Error( 'unauthorized', 'User cannot view authors for specified post type', 403 );
			}
		} elseif ( ! current_user_can( 'list_users' ) ) {
			return new WP_Error( 'unauthorized', 'User cannot view users for specified site', 403 );
		}

		$query = array(
			'number'  => $args['number'],
			'offset'  => $args['offset'],
			'order'   => $args['order'],
			'orderby' => $args['order_by'],
			'fields'  => 'ID',
		);

		if ( $authors_only ) {
			$query['capability'] = array( 'edit_posts' );
			// To-do: remove this once Jetpack requires WordPress 5.9.
			global $wp_version;
			if ( version_compare( $wp_version, '5.9-alpha', '<' ) ) {
				$query['who'] = 'authors';
				unset( $query['capability'] );
			}
		}

		if ( ! empty( $args['search'] ) ) {
			$query['search'] = $args['search'];
		}

		if ( ! empty( $args['search_columns'] ) ) {
			// this `user_search_columns` filter is necessary because WP_User_Query does not allow `display_name` as a search column
			$this->search_columns = array_intersect( $args['search_columns'], array( 'ID', 'user_login', 'user_email', 'user_url', 'user_nicename', 'display_name' ) );
			add_filter( 'user_search_columns', array( $this, 'api_user_override_search_columns' ), 10, 3 );
		}

		if ( ! empty( $args['role'] ) ) {
			$query['role'] = $args['role'];
		}

		$user_query = new WP_User_Query( $query );

		remove_filter( 'user_search_columns', array( $this, 'api_user_override_search_columns' ) );

		$return = array();
		foreach ( array_keys( $this->response_format ) as $key ) {
			switch ( $key ) {
				case 'found' :
					$return[ $key ] = (int) $user_query->get_total();
					break;
				case 'users' :
					$users = array();
					$is_multisite = is_multisite();
					foreach ( $user_query->get_results() as $u ) {
						$the_user = $this->get_author( $u, true );
						if ( $the_user && ! is_wp_error( $the_user ) ) {
							$userdata = get_userdata( $u );
							$the_user->roles = ! is_wp_error( $userdata ) ? array_values( $userdata->roles ) : array();
							if ( $is_multisite ) {
								$the_user->is_super_admin = user_can( $the_user->ID, 'manage_network' );
							}
							$users[] = $the_user;
						}
					}

					$return[ $key ] = $users;
					break;
			}
		}

		return $return;
	}

	function api_user_override_search_columns( $search_columns, $search ) {
		return $this->search_columns;
	}
}