code: public AuthenticationConfigurationBuilder saslStrength(SaslStrength... strength) {
        StringBuilder s = new StringBuilder();
        for(int i=0; i < strength.length; i++) {
           if (i > 0) {
              s.append(",");
           }
           s.append(strength[i].toString());
        }
        this.saslProperties.put(Sasl.STRENGTH, s.toString());
        return enable();
     }
docs: Sets the SASL strength property. If multiple values are specified they will determine preference order.
  Setting this property also implicitly enables authentication (see {@link #enable()}