Moving your site to SSL is often a great idea for the obvious security purposes, but also for search engine optimization (SEO), since Google now gives SSL sites a higher ranking than non-SSL sites. In this post, I’ll outline a few things to check for in your theme to make sure it’s ready for the move to SSL.

Prerequisites

If your SSL certificate has already been purchased and applied, you can follow this guide to set up your single WordPress installation for SSL, or the steps below to set up a multisite installation for it:

  1. Table wp_options: Change siteurl and home to include https in their URLs.
  2. Every site on the multisite network has its own wp_{blog_id}_options table. Update the siteurl and home fields for all of them, just as you did in step 1.
  3. Table wp_sitemeta: Similar to wp_options, there’s a siteurl field you’ll need to change here. Include https:// and the trailing slash

Or, you can use one of the plugins available on wordpress.org to do this for you.

Prepare Your Theme by Covering Your Ass(ets)

Once that’s all done, follow these steps to prepare the links to your theme’s assets (css files, javascript files, images and other media) for SSL:

1. Open the files of your theme in a text editor. Search for “http://” and scan through the results. If possible, switch any hard-coded URLs to use WP functions like get_the_permalink(), wp_get_attachment_url(), et al. to generate the correct URLs. Alternatively, you can change any hard-coded urls to protocol-relative urls – for instance, you could change http://example.com/my-image.jpg to //example.com/my-image.jpg. This allows users’ browsers to download the needed asset by prepending https to the url on an SSL site (which yours will be), or prepending http to it on a non-SSL site. If you go the protocol-relative route, just make sure the asset being linked is available at both https://example.com/my-image.jpg AND http://example.com/my-image.jpg.

2. Go through each file of your theme and make sure that wherever assets are being enqueued, they’re using the WordPress functions listed here to specify folders (directories) on your web server, and not using WP_CONTENT_DIR, WP_CONTENT_URL, WP_PLUGIN_DIR or WP_PLUGIN_URL. The functions included on that WordPress.org Codex page make use of a WordPress function named is_ssl() that checks whether or not it’s an SSL site, and returns a url with https:// if it is, or http:// if it isn’t. If your theme gets an image from /images/logo.png that’s inside of your theme’s main directory for example, the theme should include the path to that image like this: get_template_directory_uri() . ‘/images/logo.png’.

A Note about Quality Themes and Plugins

Really, if you’re using a quality theme and quality plugins, they shouldn’t be loading any assets without using those WordPress functions that perform the is_ssl() check, so you shouldn’t need to change a single thing. Performing the steps above is only to make sure that when you make the move to SSL, you’re not surprised by an image, css or javascript file, or something else not loading when you expect it to.

For a much more comprehensive guide to moving your site to SSL, including how to set up your web server to redirect http traffic to https, see this guide.

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