Zack Tollman

When deploying a TLS enabled website, you must ensure that all content loaded on the site is loaded from secure origin. 
If your content is loaded from an insecure source, the security of your whole site is compromised and modern browsers 
will downgrade your website’s security rating.
The HTTPS Mixed Content Detector plugin attempts to identify sources of mixed content warnings. The plugin will examine 
content loaded from the site when admins are viewing the site. Any content that violates the policy of loading content 
that originates from “https:” resources will trigger an error and that resource will be logged. Viewing the log will 
allow you to examine the site for any warnings and remove them before they cause problems for your website.

HTTPS Mixed Content Detector

Super useful for sites transitioning to HTTPS

Detects and logs content that will cause mixed content warnings.

Simon Waters

TLS is growing in complexity. Server Name Indication (SNI) now means HTTPS sites may be on shared IP addresses, or otherwise restricted. For these servers it is handy to be able to set desired HTTP headers without access to the web servers configuration or using .htaccess file.
This plug-in exposes controls for:
<ul>
<li>HSTS (Strict-Transport-Security)</li>
<li>HPKP (Public-Key-Pins)</li>
<li>Disabling content sniffing (X-Content-Type-Options)</li>
<li>XSS protection (X-XSS-Protection)</li>
<li>Clickjacking mitigation (X-Frame-Options in main site)</li>
<li>Expect-CT</li>
</ul>
HSTS is used to ensure that future connections to a website always use TLS, and disallowing bypass of certificate warnings for the site.
HPKP is used if you don’t want to rely solely on the Certificate Authority trust model for certificate issuance.
Disabling content sniffing is mostly of interest for sites that allow users to upload files of specific types, but that browsers might be silly enough to interpret of some other type, thus allowing unexpected attacks.
XSS protection re-enables XSS protection for the site, if the user has disabled it previously, and sets the “block” option so that attacks are not silently ignored.
Clickjacking protection is usually only relevant when someone is logged in but users requested it, presumably they have rich content outside of WordPress authentication they wish to protect.
Expect-CT is used to ensure Certificate Transparency is configured correctly.

Security Headers

Plug-in to ease the setting of TLS headers for HSTS and similar

HTTPS Mixed Content Detector vs Security Headers