gnutls_set_default_priority (session);
gnutls_certificate_type_set_priority (session, cert_type_priority);
gnutls_credentials_set (session, GNUTLS_CRD_CERTIFICATE, credentials);
gnutls_set_default_priority (session);
gnutls_certificate_type_set_priority (session, cert_type_priority);
gnutls_credentials_set (session, GNUTLS_CRD_CERTIFICATE, credentials);