This tutorial is deprecated in favour of Flexible - SSL/TLS encryption modes · Cloudflare SSL/TLS docs
Related Content:
Archive
Flexible
The connection between your visitor and Cloudflare is secured, but the connection between Cloudflare and your server is not. You will not need a certificate on your server for this mode. This option is NOT RECOMMENDED.
Flexible makes your site only partially secure - it encrypts the connection between the visitor and Cloudflare - this means they see the 
in their browser and the site leaves the impression that it’s secure! However, the connection between Cloudflare and your origin server is unencrypted and traffic can be intercepted there.
Even if you wish to pursue an insecure connection, Flexible SSL causes other problems for sites configured for HTTP at the host such as Mixed Content errors, Redirect Loops, or even completely breaking your website.
What to do about it:
You should install an SSL certificate on your server and set the SSL mode to “Full (strict)”. This fully encrypts the traffic between both the user and Cloudflare and between Cloudflare and your server.
You can use a free Let’s Encrypt certificate, generate a free Cloudflare origin certificate (SSL/TLS app), or use a paid certificate.
This is needed to make your site fully secure and is essential if you process any user submitted (e.g. logins) or personalized data through your site.
Related Content:
Why you should choose Full Strict, and only Full Strict
https://support.cloudflare.com/hc/en-us/articles/200170416-End-to-end-HTTPS-with-Cloudflare-Part-3-SSL-options
Tutorial Reference: CT-32
Reviewed: 08/22
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