OpenIdRelyingParty openid = new OpenIdRelyingParty();
IAuthenticationRequest request = openid.CreateRequest("https://www.e-contract.be/eid-idp/endpoints/openid/auth-ident");
// attribute query
FetchRequest fetchRequest = new FetchRequest();
fetchRequest.Attributes.AddRequired("http://axschema.org/namePerson");
fetchRequest.Attributes.AddRequired("http://axschema.org/eid/rrn");
request.AddExtension(fetchRequest);
request.AddExtension(new UIRequest());
request.RedirectToProvider();