@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