The Bloggers readers too are protected by Google with the help of HTTPS, the protocol that stops the traffic from being redirected outside sources that are not authorized and injected with malicious code or other malware.
Google adds HTTPS to Blogger domains; custom domains cant use it
All the users would not be offered the option to change to HTTPS at the same time, the current option is only opt-in. However, you can just follow these simple steps below, if you want to enable it:
=> Log into your Blogger account.
=> Click the blog you want to add HTTPS support to.
=> Go to your “Settings” section.
=> Find the “HTTPS settings” option and choose “Yes” from the drop-down that’s shown next to “HTTPS Availability.” It’s done.
As Google explains, it is unfortunate that blogs that run on a custom domain are not supported in this first version, and some templates and blog gadgets may encounter “mixed content errors.”
This will not be supported to the user who uses custom domain on their blogger or blogspot