Mixed Content Warning in your favourite Web Framework (it's Rails)

Upgrading to Rails v7 with esbuild wasn’t a real joy.

But when in production everything went off the rails - pun intended - a mixed active content error had me struggling.

Thankfully it was really easy to fix, by adding:

<meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests">

to the application.html.erb 😅