The following definitions are used in the description below:

• <device>

  The file system path or subsystem-specific identification string of a
  FIDO device.

• <pin>, [oldpin]

  Strings passed directly in the executed command's argument vector.

• <cred_id>

  The file system path of a file containing a FIDO credential ID in
  binary representation.

• <pubkey>

  The file system path of a file containing a public key in PEM format.

• <blobkey>

  A credential's associated CTAP 2.1 "largeBlob" symmetric key.

The following examples are provided:

• manifest

  Prints a list of configured FIDO devices.

• info <device>

  Prints information about <device>.

• reset <device>

  Performs a factory reset on <device>.

• setpin <pin> [oldpin] <device>

  Configures <pin> as the new PIN of <device>. If [oldpin] is provided,
  the device's PIN is changed from [oldpin] to <pin>.

• cred [-t es256|es384|rs256|eddsa] [-k pubkey] [-ei cred_id] [-P pin] [-T seconds] [-b blobkey] [-hruv] [-c cred_protect] <device>

  Creates a new credential on <device> and verify that the credential
  was signed by the authenticator. The device's attestation certificate
  is not verified. If option -k is specified, the credential's public
  key is stored in <pubkey>. If option -i is specified, the credential
  ID is stored in <cred_id>. The -e option may be used to add <cred_id>
  to the list of excluded credentials. If option -h is specified,
  the hmac-secret FIDO2 extension is enabled on the generated
  credential. If option -r is specified, the generated credential
  will involve a resident key. User verification may be requested
  through the -v option. If option -u is specified, the credential
  is generated using U2F (CTAP1) instead of FIDO2 (CTAP2) commands.
  The -T option may be used to enforce a timeout of <seconds>. If the
  option -b is specified, the credential's "largeBlob" key is stored in
  <blobkey>. If the option -c is specified the the generated credential
  will be bound by the specified protection policy.

• assert [-t es256|es384|rs256|eddsa] [-a cred_id] [-h hmac_secret] [-P pin] [-s hmac_salt] [-T seconds] [-b blobkey] [-puv] <pubkey> <device>

  Asks <device> for a FIDO2 assertion corresponding to [cred_id],
  which may be omitted for resident keys. The obtained assertion
  is verified using <pubkey>. The -p option requests that the user
  be present and checks whether the user presence bit was signed by the
  authenticator. The -v option requests user verification and checks
  whether the user verification bit was signed by the authenticator.
  If option -u is specified, the assertion is generated using
  U2F (CTAP1) instead of FIDO2 (CTAP2) commands. If option -s is
  specified, a FIDO2 hmac-secret is requested from the authenticator,
  and the contents of <hmac_salt> are used as the salt. If option -h
  is specified, the resulting hmac-secret is stored in <hmac_secret>.
  The -T option may be used to enforce a timeout of <seconds>. If the
  option -b specified, the credential's "largeBlob" key is stored in
  <blobkey>.

• retries <device> Get the number of PIN attempts left on <device> before lockout.

• select

  Enumerates available FIDO devices and, if more than one is present,
  simultaneously requests touch on all of them, printing information
  about the device touched.

Debugging is possible through the use of the FIDO_DEBUG environment variable. If set, libfido2 will produce a log of its transactions with the authenticator.

Additionally, an example of a WebAuthn client using libfido2 is available at https://github.com/martelletto/fido2-webauthn-client.