@deftypefun {int} {gnutls_x509_crq_get_extension_by_oid} (gnutls_x509_crq_t @var{crq}, const char * @var{oid}, unsigned @var{indx}, void * @var{buf}, size_t * @var{buf_size}, unsigned int * @var{critical})
@var{crq}: should contain a @code{gnutls_x509_crq_t}  type

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

@var{indx}: In case multiple same OIDs exist in the extensions, this
specifies which to get. 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 in case of an error.  If the certificate does not
contain the specified extension
@code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE}  will be returned.

@strong{Since:} 2.8.0
@end deftypefun