WP default registered user end point

default-registered-route.php

<?php
// https://core.trac.wordpress.org/browser/tags/4.9/src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php#L64
register_rest_route(
	$this->namespace, '/' . $this->rest_base . '/(?P<id>[\d]+)',
	array(
		'methods'             => WP_REST_Server::READABLE,
		'callback'            => array( $this, 'get_item' ),
		'permission_callback' => array( $this, 'get_item_permissions_check' ),
		'args'                => array(
		'context' => $this->get_context_param( array( 'default' => 'view' ) ),
	),			),
);
?>

get_items_permissions_check.php

<?php
/**
* Checks if a given request has access to read a user.
*
* @since 4.7.0
*
* @param WP_REST_Request $request Full details about the request.
* @return true|WP_Error True if the request has read access for the item, otherwise WP_Error object.
*/
public function get_item_permissions_check( $request ) {
	$user = $this->get_user( $request['id'] );
	if ( is_wp_error( $user ) ) {
		return $user;
	}

	$types = get_post_types( array( 'show_in_rest' => true ), 'names' );

	if ( get_current_user_id() === $user->ID ) {
		return true;
	}

	if ( 'edit' === $request['context'] && ! current_user_can( 'list_users' ) ) {
		return new WP_Error( 'rest_user_cannot_view', __( 'Sorry, you are not allowed to list users.' ), array( 'status' => rest_authorization_required_code() ) );
	} elseif ( ! count_user_posts( $user->ID, $types ) && ! current_user_can( 'edit_user', $user->ID ) && ! current_user_can( 'list_users' ) ) {
		return new WP_Error( 'rest_user_cannot_view', __( 'Sorry, you are not allowed to list users.' ), array( 'status' => rest_authorization_required_code() ) );
	}

	return true;
}
// https://core.trac.wordpress.org/browser/tags/4.9/src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php#L359