@deftypefun {int} {gnutls_x509_ext_import_key_usage} (const gnutls_datum_t * @var{ext}, unsigned int * @var{key_usage})
@var{ext}: the DER encoded extension data

@var{key_usage}: where the key usage bits will be stored

This function will return certificate's key usage, by reading the DER
data of the keyUsage X.509 extension (2.5.29.15). The key usage value will ORed
values of the: @code{GNUTLS_KEY_DIGITAL_SIGNATURE} ,
@code{GNUTLS_KEY_NON_REPUDIATION} , @code{GNUTLS_KEY_KEY_ENCIPHERMENT} ,
@code{GNUTLS_KEY_DATA_ENCIPHERMENT} , @code{GNUTLS_KEY_KEY_AGREEMENT} ,
@code{GNUTLS_KEY_KEY_CERT_SIGN} , @code{GNUTLS_KEY_CRL_SIGN} ,
@code{GNUTLS_KEY_ENCIPHER_ONLY} , @code{GNUTLS_KEY_DECIPHER_ONLY} .

@strong{Returns:} the certificate key usage, or a negative error code in case of
parsing error.  If the certificate does not contain the keyUsage
extension @code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE}  will be
returned.

@strong{Since:} 3.3.0
@end deftypefun