We had a system at work that generated 4 character alphanumeric reference numbers. Originally to avoid this they just excluded vowels from the letters but eventually they grew enough they ran out of available reference numbers so they added the vowels back in and I had to built the blacklist to avoid stuff like this happening. I reckon I probably tripped every IT filter known to man in a week long period looking for swear words in a variety of languages 😂
For most of my internal services that are sitting behind Traefik I use step-ca which basically gives you a Let’s Encrypt style certificate while working over the local network. The root CA has a long expiry (so might not be what you want if your goal Is a short lived root CA) but the actual certificates for each service are short lived (a touch over 24 hours from memory?)