int gnutls_x509_crt_get_extension_by_oid(gnutls_x509_crt_t cert, const char * oid, int indx, void * buf, size_t * sizeof_buf, unsigned int * critical);
should contain a gnutls_x509_crt_t structure
const char * oid
holds an Object Identified in null terminated string
In case multiple same OIDs exist in the extensions, this specifies which to send. Use zero to get the first one.
void * buf
a pointer to a structure to hold the name (may be null)
size_t * sizeof_buf
initially holds the size of buf
unsigned int * 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.
On success, GNUTLS_E_SUCCESS (zero) is returned,
otherwise an error code is returned. If the certificate does not
contain the specified extension
GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE will be returned.