@deftypefun {int} {gnutls_x509_ext_export_key_usage} (unsigned int @var{usage}, gnutls_datum_t * @var{ext})
@var{usage}: an ORed sequence of the GNUTLS_KEY_* elements.

@var{ext}: The DER-encoded extension data; must be freed using @code{gnutls_free()} .

This function will convert the keyUsage bit string to a DER
encoded PKIX extension. The  @code{ext} data will be allocated using
@code{gnutls_malloc()} .

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value.

@strong{Since:} 3.3.0
@end deftypefun