There are a lot of edge case characters around visually indistinguishable names. If that is a concern usernames should use a restricted known character sets instead of trying to block specific characters. You likely should also treat lookalike characters as equivalents when checking for username overlap.
It can still have issues with potential attacks that would redirect your client to a system outside of the VPN. It would prevent MitM but not complete replacement.
Likely you needed to include the intermediate cert chain. Let’s encrypt sets that up automatically so it’s quite a bit easier to get right.
The plastic and wire twist ties that come on cables would work too.
The expression syntax for the GNU find command is very powerful. I would expect that it is up to the task. If you don’t have the GNU find command with it’s extensions I could see how it’s would be difficult.
From what I’ve read is not authentication bypass, it’s a RCE using certificates to deliver the payload. If a specific signature is found it runs the code that was sent in place of the signing public key. It also means that only someone who has the ability to generate that specific key signature could use the RCE.
There were some other bits that looked like they could have been placed to enable compromising other build systems in the future when they checked for xz support.