code: public static boolean serverSupportsSecretKeyBackups(XMPPConnection connection)
              throws XMPPException.XMPPErrorException, SmackException.NotConnectedException, InterruptedException,
              SmackException.NoResponseException {
          return ServiceDiscoveryManager.getInstanceFor(connection)
                  .serverSupportsFeature(PubSubFeature.access_whitelist.toString());
      }
docs: Determine, if we can sync secret keys using private PEP nodes as described in the XEP.
  Requirements on the server side are support for PEP and support for the whitelist access model of PubSub.
  
  @see <a href="https://xmpp.org/extensions/xep-0373.html#synchro-pep">XEP-0373 §5</a>
  
  @param connection XMPP connection
  @return true, if the server supports secret key backups, otherwise false.
  @throws XMPPException.XMPPErrorException in case of an XMPP protocol error.
  @throws SmackException.NotConnectedException if we are not connected.
  @throws InterruptedException if the thread is interrupted.
  @throws SmackException.NoResponseException if the server doesn't respond.