NAME

       libssh2_userauth_publickey_sk - authenticate a session with a FIDO2 authenticator

SYNOPSIS

       #include <libssh2.h>

       int
       libssh2_userauth_publickey_sk(LIBSSH2_SESSION *session,
                                     const char *username,
                                     size_t username_len,
                                     const unsigned char *publickeydata,
                                     size_t publickeydata_len,
                                     const char *privatekeydata,
                                     size_t privatekeydata_len,
                                     const char *passphrase,
                                     LIBSSH2_USERAUTH_SK_SIGN_FUNC((*sign_callback)),
                                     void **abstract);

CALLBACK

       #define LIBSSH2_SK_PRESENCE_REQUIRED     0x01
       #define LIBSSH2_SK_VERIFICATION_REQUIRED 0x04

       typedef struct _LIBSSH2_SK_SIG_INFO {
           uint8_t flags;
           uint32_t counter;
           unsigned char *sig_r;
           size_t sig_r_len;
           unsigned char *sig_s;
           size_t sig_s_len;
       } LIBSSH2_SK_SIG_INFO;

       int name(LIBSSH2_SESSION *session, LIBSSH2_SK_SIG_INFO *sig_info,
                const unsigned char *data, size_t data_len, int algorithm,
                uint8_t flags, const char *application,
                const unsigned char *key_handle, size_t handle_len,
                void **abstract);

DESCRIPTION

       session - Session instance as returned by libssh2_session_init_ex(3)

       username - Name of user to attempt authentication for.

       username_len - Length of username parameter.

       publickeydata  -  Buffer containing the contents of a public key file. If NULL, the public
       key will be extracted from the privatekeydata. When using certificate authentication, this
       buffer should contain the public certificate data.

       publickeydata_len - Length of public key data.

       privatekeydata - Buffer containing the contents of a private key file.

       privatekeydata_len - Length of private key data.

       passphrase - Passphrase to use when decoding private key file.

       sign_callback - Callback to communicate with FIDO2 authenticator.

       abstract - User-provided data to pass to callback.

       Attempt  FIDO2  authentication.  using  either the sk-ssh-ed25519@openssh.com or sk-ecdsa-
       sha2-nistp256@openssh.com key exchange algorithms.

       This function is only supported when libssh2 is backed by OpenSSL.

CALLBACK DESCRIPTION

       session - Session instance as returned by libssh2_session_init_ex(3)

       sig_info - Filled in by the callback with the signature and accompanying information  from
       the authenticator.

       data - The data to sign.

       data_len - The length of the data parameter.

       algorithm - The signing algorithm to use. Possible values are LIBSSH2_HOSTKEY_TYPE_ED25519
       and LIBSSH2_HOSTKEY_TYPE_ECDSA_256.

       flags   -    A    bitmask    specifying    options    for    the    authenticator.    When
       LIBSSH2_SK_PRESENCE_REQUIRED   is   set,   the   authenticator   requires  a  touch.  When
       LIBSSH2_SK_VERIFICATION_REQUIRED is set, the authenticator requires a PIN.   Many  servers
       and authenticators do not work properly when LIBSSH2_SK_PRESENCE_REQUIRED is not set.

       application  -  A user-defined string to use as the RP name for the authenticator. Usually
       "ssh:".

       key_handle - The key handle to use for the authenticator's allow list.

       handle_len - The length of the key_handle parameter.

       abstract - User-defined data. When a PIN is required, use this to pass in the  PIN,  or  a
       function pointer to retrieve the PIN.

       The  sign_callback  is  responsible  for  communicating with the hardware authenticator to
       generate a signature. On  success,  the  signature  information  must  be  placed  in  the
       `sig_info  sig_info parameter and the callback must return 0. On failure, it should return
       a negative number.

       The fields of the LIBSSH2_SK_SIG_INFO are as follows.

       flags - A bitmask specifying options for the authenticator. This should be read  from  the
       authenticator and not merely copied from the flags parameter to the callback.

       counter - A value returned from the authenticator.

       sig_r  -  For Ed25519 signatures, this contains the entire signature, as returned directly
       from the authenticator. For ECDSA  signatures,  this  contains  the  r  component  of  the
       signature in a big-endian binary representation. For both algorithms, use LIBSSH2_ALLOC to
       allocate memory. It will be freed by the caller.

       sig_r_len - The length of the sig_r parameter.

       sig_s - For ECDSA signatures, this contains the s component of the  signature  in  a  big-
       endian  binary  representation.  Use LIBSSH2_ALLOC to allocate memory. It will be freed by
       the caller. For Ed25519 signatures, set this to NULL.

       sig_s_len - The length of the sig_s parameter.

RETURN VALUE

       Return 0 on success or negative on failure. It returns LIBSSH2_ERROR_EAGAIN when it  would
       otherwise  block.  While  LIBSSH2_ERROR_EAGAIN  is  a  negative number, it is not really a
       failure per se.

ERRORS

       Some of the errors this function may return include:

       LIBSSH2_ERROR_ALLOC - An internal memory allocation call failed.

       LIBSSH2_ERROR_SOCKET_SEND - Unable to send data on socket.

       LIBSSH2_ERROR_AUTHENTICATION_FAILED - failed, invalid username/key.

AVAILABILITY

       Added in libssh2 1.10.0

SEE ALSO

       libssh2_session_init_ex(3)