HTTP Strict Transport Security (HSTS) can substantially improve the security of your website. However, there are important considerations to keep in mind when enabling HSTS:
HTTPS (SSL) must be enabled in order to use HSTS.
If you turn on HSTS and do not have HTTPS for your website, browsers will not accept the HSTS setting.
If you have HSTS enabled and leave CloudFlare, you need continue to support HTTPS through a new service provider otherwise your site will become inaccessible to visitors until you support HTTPS again.
If you turn off CloudFlare’s HTTPS while HSTS is enabled, and you don't have a valid SSL certificate on your origin server, your website will become inaccessible to visitors.
Note: Disabling CloudFlare’s HTTP can be done in several ways: Grey clouding a subdomain in your DNS records, “Pausing” the CloudFlare service, or having a misconfigured custom SSL certificate through your CloudFlare dashboard (e.g., invalid SSL certificates, expired certificates, or mismatched host names).
If you need to disable HTTPS on your domain, you must first disable HSTS in your CloudFlare dashboard and wait for the max-age to lapse to guarantee that every browser is aware of this change before you can disable HTTPS. The average max-age is six months (you can set the max-age in the next step). If you remove HTTPS before disabling HSTS your website will become inaccessible to visitors for up to the max-age or until you support HTTPS again. Because disabling HTTPS on an HSTS enabled website can have these consequences, we strongly suggest that you have a committed HTTPS service in place before enabling this feature.
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