The ssh-sk-helper client API gives us a nice place to disable
security key support when it is wasn't enabled at compile time,
so we don't need to check everywere.
Also, verification of security key signatures can remain enabled
all the time - it has no additional dependencies. So sshd can
accept security key pubkeys in authorized_keys, etc regardless of
the host's support for dlopen, etc.
This is populated during signature verification with additional fields
that are present in and covered by the signature. At the moment, it is
only used to record security key-specific options, especially the flags
field.
with and ok markus@
OpenBSD-Commit-ID: 338a1f0e04904008836130bedb9ece4faafd4e49
better match ec25519-sk keys. Discussed with markus@ and Sebastian Kinne
NB. if you are depending on security keys (already?) then make sure you
update both your clients and servers.
OpenBSD-Commit-ID: 53d88d8211f0dd02a7954d3af72017b1a79c0679
