docs: @Override
      public byte[] initSecContext ( byte[] inputBuf, int offset, int len ) throws CIFSException {
          SpnegoToken resp;
          if ( this.completed ) {
              throw new CIFSException("Already complete");
          }
          else if ( len == 0 ) {
              resp = initialToken();
          }
          else {
              resp = negotitate(inputBuf, offset, len);
          }
  
          if ( resp == null ) {
              return null;
          }
          return resp.toByteArray();
      }