code: public Payload setClassReference(String classReference) {
          this.classReference = classReference;
          this.put(PayloadConstants.CLASS_REFERENCE, classReference);
          return this;
      }
docs: Sets the authentication context class reference or {@code null} for none.
  
  <p>
  Overriding is only supported for the purpose of calling the super implementation and changing
  the return type, but nothing else.
  </p>