code: protected String toBaseURI(String uri) {
      LoaEnum loa = LoaEnum.parse(uri);
      if (loa != null && loa.isSignatureMessageUri()) {
        return LoaEnum.minusSigMessage(loa).getUri();
      }
      return uri;
    }
docs: Given an URI its base form is returned. This means that the URI minus any potential sigmessage extension.
  
  @param uri
  the URI to convert
  @return the base URI