An url which opens both in www,non www and both http and https is said to be canonical url

which is very useful for your website SEO,because canonical url indicate's your site is checked there is no duplicate content.

authoritative is utilized to avoid punishments by google for copy content. Sanctioned label show to google what one is your lord page whether your single page is open my multipal url.

A canonical link element is an HTML element that helps webmasters prevent duplicate content issues in search engine optimization by specifying the "canonical" or "preferred" version of a web page.

A canonical URL is the URL of the best representative page from a group of duplicate web pages.