Once you've run a crawl of your site in the Site Audit tool, you might see a 'Canonical from HTTP to HTTPS' notice in the report under Internal pages menu:

This notice indicates that HTTP pages (non-secure) on your website with the canonical link is pointing to an HTTPS page (secure).
​

Canonical link is placed in the header of the document and looks as follows:

<https://ahrefs.com/blog/seo-metrics/>

A rel="canonical" attribute is used to help solve duplicate content issues. Pages with duplicate or similar content may confuse search engines, as they wouldn't know which of the 2 similar pages deserve to rank. This is where canonical URLs come in handy. 

HTTPS is one of the ranking signals for Google. Therefore, It is recommended to adopt HTTPS across your website.

The HTTPS protocol is considered to be better as it is secure - it encrypts the information between your browser and the website. 

Customers are also more likely to trust and complete purchases from your site if you're using HTTPS.
​
​Related: