Your network authentication should not be a fun game or series of Rube Goldberg contraptions.
Use-cases:
1. helps auto-ban hosts doing port-scans or using online vulnerability scanners
2. helps reduce further ingress for a few minutes as the hostile sees the site is "down". Generally, try to waste as much of a problem users time as possible, as it changes the economics of breaking networked systems.
3. the firewall rule-trigger delay means hostiles have a harder time guessing which action triggered a IP ban. If every login attempt costs 3 days, folks would have to be pretty committed to breaking into a simple website.
4. keeps failed login log noise to a minimum, so spotting actual problems is easier
5. Easier to forensically analyze the remote packet stream when doing a packet dump tap, as only the key user traffic is present
6. buys time to patch vulnerable code when zero day exploits hits other hosts exposed services
7. most administrative ssh password-less key traffic should be tunneled over SSL web services, and thus attackers have a greater challenge figuring out if dynamic service-switching is even active
People that say it isn't a "security policy" are somewhat correct, but are also naive when it comes to the reality of dealing with nuisance web traffic.
Fail2ban is slightly different in that it is for setting up tripwires for failed email logins, and known web-vulnerability scanners etc. Then whispering that IP ban period to the firewall (must override the default config.)
Finally, if the IP address for some application login session changes more than 5 times an hour, one should also whisper a ban to the firewalls. These IP ban rules are often automatically shared between groups to reduce forum spam, VoIP attacks, and problem users. Popular cloud-based VPN/proxies/Tor-exit-nodes run out of unique IPs faster than most assume.
Have a nice day, =3
Your services should simply be unreachable over anything but wireguard (or another secure VPN option).
However, even with all those choices, “port knocking” still wouldn’t be a solution for anything.
[edit]
Are you just searching for random WireGuard CVEs now?
CVE-2024-26950 was a *local-only* DoS and potential UaF requiring privileged access to wireguard netlink sockets.
<edit>
Firewall administrative network port traffic priority is important for systems under abnormal stress.
Open source tools are good at actually doing the job, as long as it's a programmer type of job. We've known how to do unbreakable encryption for decades now. Even PGP still hasn't been broken. Wireguard is one of those solutions in the "so simple it has obviously no bugs" category - that's actually what differentiates it from protocols like OpenVPN.
Think about the recent satellite listening talk at DEFCON and how that massive data leak could have been prevented by even just running your traffic through AES with a fixed key of the CEO's cat's name on a Raspberry Pi, but that's a non-corporate solution and so not acceptable to a corporation, who will only ever consider enabling encryption if it comes with a six figure per year license fee which is what the satellite box makers charged for it. Corporations, as a rule, are only barely competent enough to make money and no more.
I don't like or trust OpenVPN. I'd sooner expose OpenSSH itself, which has really a pretty stunning security track record.
A lot of VPN installations are simply done wrong, and it only takes 1 badly configured client or cloud side-channel to make it pointless. IPSec is not supported on a lot of LANs, and 5k users would prove rather expensive to administer.
Also, GnuPG Kyber will not be supported by VPN software anytime soon, but it would be super cool if it happens. =3
The biggest weakness in VPN is client-side cross-network leaks.
IPSec is simply a luxury if the LAN supports it, but also an administrative nightmare for >5k users. =3