Source

File: wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php

public function prepare_item_for_response( $user, $request ) {

		$data   = array();
		$fields = $this->get_fields_for_response( $request );

		if ( in_array( 'id', $fields, true ) ) {
			$data['id'] = $user->ID;
		}

		if ( in_array( 'username', $fields, true ) ) {
			$data['username'] = $user->user_login;
		}

		if ( in_array( 'name', $fields, true ) ) {
			$data['name'] = $user->display_name;
		}

		if ( in_array( 'first_name', $fields, true ) ) {
			$data['first_name'] = $user->first_name;
		}

		if ( in_array( 'last_name', $fields, true ) ) {
			$data['last_name'] = $user->last_name;
		}

		if ( in_array( 'email', $fields, true ) ) {
			$data['email'] = $user->user_email;
		}

		if ( in_array( 'url', $fields, true ) ) {
			$data['url'] = $user->user_url;
		}

		if ( in_array( 'description', $fields, true ) ) {
			$data['description'] = $user->description;
		}

		if ( in_array( 'link', $fields, true ) ) {
			$data['link'] = get_author_posts_url( $user->ID, $user->user_nicename );
		}

		if ( in_array( 'locale', $fields, true ) ) {
			$data['locale'] = get_user_locale( $user );
		}

		if ( in_array( 'nickname', $fields, true ) ) {
			$data['nickname'] = $user->nickname;
		}

		if ( in_array( 'slug', $fields, true ) ) {
			$data['slug'] = $user->user_nicename;
		}

		if ( in_array( 'roles', $fields, true ) ) {
			// Defensively call array_values() to ensure an array is returned.
			$data['roles'] = array_values( $user->roles );
		}

		if ( in_array( 'registered_date', $fields, true ) ) {
			$data['registered_date'] = gmdate( 'c', strtotime( $user->user_registered ) );
		}

		if ( in_array( 'capabilities', $fields, true ) ) {
			$data['capabilities'] = (object) $user->allcaps;
		}

		if ( in_array( 'extra_capabilities', $fields, true ) ) {
			$data['extra_capabilities'] = (object) $user->caps;
		}

		if ( in_array( 'avatar_urls', $fields, true ) ) {
			$data['avatar_urls'] = rest_get_avatar_urls( $user );
		}

		if ( in_array( 'meta', $fields, true ) ) {
			$data['meta'] = $this->meta->get_value( $user->ID, $request );
		}

		$context = ! empty( $request['context'] ) ? $request['context'] : 'embed';

		$data = $this->add_additional_fields_to_object( $data, $request );
		$data = $this->filter_response_by_context( $data, $context );

		// Wrap the data in a response object.
		$response = rest_ensure_response( $data );

		$response->add_links( $this->prepare_links( $user ) );

		/**
		 * Filters user data returned from the REST API.
		 *
		 * @since 4.7.0
		 *
		 * @param WP_REST_Response $response The response object.
		 * @param WP_User          $user     User object used to create response.
		 * @param WP_REST_Request  $request  Request object.
		 */
		return apply_filters( 'rest_prepare_user', $response, $user, $request );
	}