Blucube

If your site has an SSL certificate you might find that you can access the site via both SSL (https) and non-SSL (http) URLs. This is a bad idea for security, and for SEO, as it can look like duplicate content on different URLs.
The answer to this is to redirect requests to non-SSL (http) URLs over to their SSL (https) equivalents using something called a 301 redirect. This tells the client (and search engines) that the resource they are looking for should always be accessed over SSL. This plugin offers two methods to achieve this:
<ul>
<li>By intercepting WordPress pages at header time, and if they are not already being requested over HTTPS sending a 301 redirect header, or</li>
<li>By adding mod_rewrite rules in the .htaccess file to redirect all requests to their HTTPS equivalents using 301 redirects.</li>
</ul>
Optionally, this plugin can also set <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Strict-Transport-Security" rel="nofollow ugc">HSTS</a> headers for you, and make sure that all requests use the same hostname (i.e. fixing the issue where many sites can be accessed using both www. and non-www. URLs).

Simple SSL Redirects

Lightweight plugin to ensure access via SSL/HTTPS. Uses 301 (permanent) redirects for SEO benefits. Optionally sets HSTS and forces canonical domain.

Jay Suthar

BoundaryGuard Headers enforces modern HTTP security headers to harden your WordPress site against XSS, clickjacking, mixed content, and cross-origin attacks.
Key Features:
<ul>
<li>Essential Protection: Adds X-Frame-Options, X-Content-Type-Options, Referrer-Policy, and Permissions-Policy to reduce attack surface and prevent clickjacking.</li>
<li>HSTS (Strict Transport Security): Forces HTTPS connections to help prevent protocol downgrade and man-in-the-middle attacks.</li>
<li>Advanced Isolation (COOP/COEP): Enables Cross-Origin-Opener-Policy and Cross-Origin-Embedder-Policy to improve cross-origin isolation and mitigate certain side-channel attacks.</li>
<li>Content Security Policy (CSP): One of the strongest defenses against XSS. Includes a dashboard-based CSP builder with preset options to whitelist trusted sources for scripts, styles, images, and more.</li>
<li>CSP Report-Only Mode: Test your policy safely without blocking content.</li>
<li>Server Header Hardening: Removes or limits exposure of headers such as <code>X-Powered-By</code> and <code>Server</code>.</li>
<li>Lightweight and Fast: Uses PHP headers for broad server compatibility and minimal performance impact.</li>
<li>No <code>.htaccess</code> Editing Required: Works without modifying server configuration files.</li>
</ul>
Designed for developers and site owners who want stronger security without unnecessary complexity.
<h3>External Services</h3>
This plugin provides a Content Security Policy (CSP) builder. To assist users, it includes “Preset Buttons” that allow users to quickly add domain names to their own CSP whitelist.
This plugin DOES NOT connect to, load data from, or send data to these services automatically. The following third-party domains are referenced as presets within the admin dashboard for whitelisting purposes: 
* Google Analytics (www.google-analytics.com) – Used for tracking whitelisting. [Privacy: https://policies.google.com/privacy] 
* Google Tag Manager (www.googletagmanager.com) – Used for tag management. [Privacy: https://policies.google.com/privacy] 
* Stripe (js.stripe.com, api.stripe.com) – Used for payment processing. [Privacy: https://stripe.com/privacy] 
* Facebook (www.facebook.com, connect.facebook.net) – Used for social embeds. [Privacy: https://www.facebook.com/policy.php] 
* YouTube (www.youtube.com, i.ytimg.com) – Used for video embeds. [Privacy: https://policies.google.com/privacy] 
* Vimeo (player.vimeo.com) – Used for video embeds. [Privacy: https://vimeo.com/privacy] 
* Gravatar (secure.gravatar.com) – Used for user avatars. [Privacy: https://automattic.com/privacy/]

BoundaryGuard Headers

Automatically enforces essential HTTP security headers to protect your site from XSS, clickjacking, and protocol downgrade attacks.

Simple SSL Redirects vs BoundaryGuard Headers