code: @Override
    public List<String> getPossibleAuthnContextClassRefs(ProfileRequestContext<?, ?> context, boolean signMessage)
        throws ExternalAutenticationErrorCodeException {
  
      AuthnContextClassContext authnContextContext = this.getAuthnContextClassContext(context);
      List<String> possibleUris = null;
      
      if (signMessage) {
        possibleUris = authnContextContext.getAuthnContextClassRefs()
            .stream()
            .filter(u -> this.isSignMessageURI(u))
            .map(u -> this.toBaseURI(u))
            .collect(Collectors.toList());
      }
      if (possibleUris == null || possibleUris.isEmpty()) {
        possibleUris = authnContextContext.getAuthnContextClassRefs()
            .stream()
            .filter(u -> !this.isSignMessageURI(u))
            .collect(Collectors.toList());
      }
      
      if (possibleUris.isEmpty()) {
        final String msg = "No AuthnContext URI:s can be used to authenticate user";
        log.info("{} - can not proceed [{}]", msg, this.getLogString(context));
        throw new ExternalAutenticationErrorCodeException(AuthnEventIds.REQUEST_UNSUPPORTED, msg);
      }
  
      return possibleUris;
    }
docs: {@inheritDoc}