docs: public AuthenticationConfigurationBuilder saslQop(SaslQop... qop) {
        StringBuilder s = new StringBuilder();
        for(int i=0; i < qop.length; i++) {
           if (i > 0) {
              s.append(",");
           }
           s.append(qop[i].toString());
        }
        this.saslProperties.put(Sasl.QOP, s.toString());
        return enable();
     }