docs: @Nonnull
    public DigestAuthServerBuilder setAlgorithm (@Nonnull final String sAlgorithm)
    {
      if (!HttpStringHelper.isToken (sAlgorithm))
        throw new IllegalArgumentException ("The passed algorithm is not a valid token: " + sAlgorithm);
  
      m_sAlgorithm = sAlgorithm;
      return this;
    }