@deftypefun {int} {gnutls_x509_crt_get_extension_by_oid} (gnutls_x509_crt_t @var{cert}, const char * @var{oid}, unsigned @var{indx}, void * @var{buf}, size_t * @var{buf_size}, unsigned int * @var{critical})

@var{cert}: should contain a @code{gnutls_x509_crt_t}  type

@var{oid}: holds an Object Identified in null terminated string

@var{indx}: In case multiple same OIDs exist in the extensions, this specifies which to send. Use (0) to get the first one.

@var{buf}: a pointer to a structure to hold the name (may be null)

@var{buf_size}: initially holds the size of  @code{buf} 

@var{critical}: will be non-zero if the extension is marked as critical

This function will return the extension specified by the OID in the

certificate.  The extensions will be returned as binary data DER

encoded, in the provided buffer.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,

otherwise a negative error code is returned. If the certificate does not

contain the specified extension

GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE will be returned.

@end deftypefun