I never thought it would happen to me. I was careful, I prepared well in advance, I even had multiple environments to test things out in... I got caught out by clutter. I had updated the correct file in the development environment, but updated a file with the same name in a slightly different location in production. A brief check of the system with the new certificate in place seemed fine - the certificate didn't look like it was due to expire on the known expiry date. That's the problem with an expiring CA certificate - it's not front and centre showing up as something you need to be concerned about. The chain of trust is a bit less visible, you have to click through to see the details. In the heat of the moment, troubleshooting what might have gone wrong with the setup I even repeated the mistake of copying the file in the wrong location.
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