@deftypefun {int} {gnutls_x509_crt_get_extension_oid} (gnutls_x509_crt_t @var{cert}, unsigned @var{indx}, void * @var{oid}, size_t * @var{oid_size})
@var{cert}: should contain a @code{gnutls_x509_crt_t} type
@var{indx}: Specifies which extension OID to send. Use (0) to get the first one.
@var{oid}: a pointer to a structure to hold the OID (may be null)
@var{oid_size}: initially holds the size of @code{oid}
This function will return the requested extension OID in the certificate.
The extension OID will be stored as a string in the provided buffer.
The @code{oid} returned will be null terminated, although @code{oid_size} will not
account for the trailing null.
@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS} (0) is returned,
otherwise a negative error code is returned. If you have reached the
last extension available @code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE}
will be returned.
@end deftypefun