Last month I delved into security headers including Content Security Policies and added a bunch of them to my website. I did this to learn more about website security and improve my websites' security.
But I learnt that I had inadvertently broken some things on my site - this wasn't obvious because I have a cobbled together ServiceWorker which meant I didn't see the things that had stopped working - namely images and sliders.
I spent a few hours applying fixes to my website to comply with the Content Security Policies I implemented a few weeks ago and at the same time improved my websites' performance and usability.
The issue I had is that its either all or nothing. So you cant have any inline JS or CSS. The JS was a quick fix - I needed to move it to a file. But I use CSS to apply background images to components via the CMS. So I needed to move that to the CSS file and use a class to apply a chosen background image.
One of the issues I had was that all inline CSS is blocked, only linked to CSS files will be applied to my website, this meant that I had to change how I did the background images for the hero section. I was able to add the image via front matter or the CMS, which would then be added to the hero section using inline CSS.
I now have a list of modifier classes I add to the hero section that chooses the type of background image I use. I have been using the same image for code related blog posts, for example, so it made sense to move that to a class in my main stylesheet. I can always create new ones with different background images when I need them.
You can use the "inline-unsafe" CSP rule to allow inline styling, but this makes it, as the name suggests, not safe to use. I think with my limited security knowledge that if you disallow inline scripts, it would be safe to allow inline styling - I can imagine the only way for someone to change the styling of your website would be via an injected script.
I had a testimonials slider on my homepage - it used a slider script and some custom JS to customise the slider. I started by moving the custom code from being inline into a JS file and linking to it, but I was struggling to generate a SHA (Secure Hash Algorithm) for the slider library.
Now I show a random testimonial on the homepage, with a new one being randomly shown every time there is a new build of my website.
I also removed the image slider from portfolio projects. The images now are shown in a column with project details on the right which I also applied position sticky to the project detail sidebar to it stays with the user as they scroll down to see all the project images.
I enjoyed it this - now my website fully complies with very secure CSPs. It's more secure, has better performance and better for users. Win win.