Fix ssh-config short-lived-cert for subpath-ed hostnames

[jeslinmx]

Fixes #923

[ajvpot]

Is this subject to a race condition when configuring a host name like "*.mycompany.com"? I think connecting to two hosts at the same time with this patch could cause the wrong cert to be used.

[jeslinmx]

Sorry, but I don't think I understand the potential problem you're describing. Could you give an example of 2 hostnames that might create such a clash?

[ajvpot]

Sure, In this case I have configured access like so:

alex@Alexs-MacBook-Pro> cloudflared access ssh-config --hostname '*.mycorp.com' --short-lived-cert
Add to your /Users/alex/.ssh/config:

Match host *.mycorp.com exec "/Users/alex/bin/cloudflared access ssh-gen --hostname %h"
  ProxyCommand /Users/alex/bin/cloudflared access ssh --hostname %h
  IdentityFile ~/.cloudflared/%h-cf_key
  CertificateFile ~/.cloudflared/%h-cf_key-cert.pub

After this change the config would be:

Match host *.mycorp.com exec "/Users/alex/bin/cloudflared access ssh-gen --hostname %h"
  ProxyCommand /Users/alex/bin/cloudflared access ssh --hostname %h
  IdentityFile ~/.cloudflared/*.mycorp.com-cf_key
  CertificateFile ~/.cloudflared/*.mycorp.com-cf_key-cert.pub

Which may cause problems when SSHing to multiple hosts that match that pattern and use different SSH CA public keys at the same time.