NAME

     fido_assert_set_authdata, fido_assert_set_authdata_raw, fido_assert_set_clientdata,
     fido_assert_set_clientdata_hash, fido_assert_set_count, fido_assert_set_extensions,
     fido_assert_set_hmac_salt, fido_assert_set_hmac_secret, fido_assert_set_up, fido_assert_set_uv,
     fido_assert_set_rp, fido_assert_set_sig — set parameters of a FIDO2 assertion

SYNOPSIS

     #include <fido.h>

     typedef enum {
             FIDO_OPT_OMIT = 0, /* use authenticator's default */
             FIDO_OPT_FALSE,    /* explicitly set option to false */
             FIDO_OPT_TRUE,     /* explicitly set option to true */
     } fido_opt_t;

     int
     fido_assert_set_authdata(fido_assert_t *assert, size_t idx, const unsigned char *ptr, size_t len);

     int
     fido_assert_set_authdata_raw(fido_assert_t *assert, size_t idx, const unsigned char *ptr, size_t len);

     int
     fido_assert_set_clientdata(fido_assert_t *assert, const unsigned char *ptr, size_t len);

     int
     fido_assert_set_clientdata_hash(fido_assert_t *assert, const unsigned char *ptr, size_t len);

     int
     fido_assert_set_count(fido_assert_t *assert, size_t n);

     int
     fido_assert_set_extensions(fido_assert_t *assert, int flags);

     int
     fido_assert_set_hmac_salt(fido_assert_t *assert, const unsigned char *ptr, size_t len);

     int
     fido_assert_set_hmac_secret(fido_assert_t *assert, size_t idx, const unsigned char *ptr, size_t len);

     int
     fido_assert_set_up(fido_assert_t *assert, fido_opt_t up);

     int
     fido_assert_set_uv(fido_assert_t *assert, fido_opt_t uv);

     int
     fido_assert_set_rp(fido_assert_t *assert, const char *id);

     int
     fido_assert_set_sig(fido_assert_t *assert, size_t idx, const unsigned char *ptr, size_t len);

DESCRIPTION

     The fido_assert_set_authdata set of functions define the various parameters of a FIDO2 assertion, allowing
     a fido_assert_t type to be prepared for a subsequent call to fido_dev_get_assert(3) or
     fido_assert_verify(3).  For the complete specification of a FIDO2 assertion and the format of its
     constituent parts, please refer to the Web Authentication (webauthn) standard.

     The fido_assert_set_count() function sets the number of assertion statements in assert to n.

     The fido_assert_set_authdata() and fido_assert_set_sig() functions set the authenticator data and signature
     parts of the statement with index idx of assert to ptr, where ptr points to len bytes.  A copy of ptr is
     made, and no references to the passed pointer are kept.  Please note that the first assertion statement of
     assert has an idx of 0.  The authenticator data passed to fido_assert_set_authdata() must be a CBOR-encoded
     byte string, as obtained from fido_assert_authdata_ptr().  Alternatively, a raw binary blob may be passed
     to fido_assert_set_authdata_raw().

     The fido_assert_set_clientdata_hash() function sets the client data hash of assert to ptr, where ptr points
     to len bytes.  A copy of ptr is made, and no references to the passed pointer are kept.

     The fido_assert_set_clientdata() function allows an application to set the client data hash of assert by
     specifying the assertion's unhashed client data.  This is required by Windows Hello, which calculates the
     client data hash internally.  For compatibility with Windows Hello, applications should use
     fido_assert_set_clientdata() instead of fido_assert_set_clientdata_hash().

     The fido_assert_set_rp() function sets the relying party id of assert, where id is a NUL-terminated UTF-8
     string.  The content of id is copied, and no references to the passed pointer are kept.

     The fido_assert_set_extensions() function sets the extensions of assert to the bitmask flags.  At the
     moment, only the FIDO_EXT_CRED_BLOB, FIDO_EXT_HMAC_SECRET, and FIDO_EXT_LARGEBLOB_KEY extensions are
     supported.  If flags is zero, the extensions of assert are cleared.

     The fido_assert_set_hmac_salt() and fido_assert_set_hmac_secret() functions set the hmac-salt and hmac-
     secret parts of assert to ptr, where ptr points to len bytes.  A copy of ptr is made, and no references to
     the passed pointer are kept.  The HMAC Secret (hmac-secret) Extension is a CTAP 2.0 extension.  The
     fido_assert_set_hmac_secret() function is normally only useful when writing tests.

     The fido_assert_set_up() and fido_assert_set_uv() functions set the up (user presence) and uv (user
     verification) attributes of assert.  Both are FIDO_OPT_OMIT by default, allowing the authenticator to use
     its default settings.

     Use of the fido_assert_set_authdata set of functions may happen in two distinct situations: when asking a
     FIDO2 device to produce a series of assertion statements, prior to fido_dev_get_assert(3) (i.e, in the
     context of a FIDO2 client), or when verifying assertion statements using fido_assert_verify(3) (i.e, in the
     context of a FIDO2 server).

     For a complete description of the generation of a FIDO2 assertion and its verification, please refer to the
     FIDO2 specification.  An example of how to use the fido_assert_set_authdata set of functions can be found
     in the examples/assert.c file shipped with libfido2.

RETURN VALUES

     The fido_assert_set_authdata functions return FIDO_OK on success.  The error codes returned by the
     fido_assert_set_authdata set of functions are defined in <fido/err.h>.

SEE ALSO

     fido_assert_allow_cred(3), fido_assert_verify(3), fido_dev_get_assert(3)