RequestBuilder request = new RequestBuilder(VERIFY_LINK, HttpMethod.POST);
request.addParam("assertion", assertion);
request.addParam("audience", audience);
HttpResponse response = request.execute();
if (response.getResponseCode() != HttpServletResponse.SC_OK)
throw new IllegalStateException("Bad response code: " + response.getResponseCode());
Assertion result = MAPPER.readValue(response.getContentStream(), Assertion.class);