code: public Account createAccount(String email, String clientId, String clientSecret) throws HelloSignException {
          HttpClient client = httpClient.withAuth(auth).withPostField(Account.ACCOUNT_EMAIL_ADDRESS, email);
          if (clientId != null && clientSecret != null) {
              client = client.withPostField(CLIENT_ID, clientId).withPostField(CLIENT_SECRET, clientSecret);
          }
          JSONObject response = client.post(BASE_URI + ACCOUNT_CREATE_URI).asJson();
          JSONObject copy;
          try {
              copy = new JSONObject(response.toString());
          } catch (JSONException e) {
              throw new HelloSignException(e);
          }
          OauthData data = new OauthData(copy);
          Account account = new Account(response);
          account.setOauthData(data);
          return account;
      }
docs: Creates a new HelloSign account and provides OAuth app credentials to
  automatically generate an OAuth token with the user Account response.
  
  @param email String New user's email address
  @param clientId String Client ID
  @param clientSecret String App secret
  @return Account New user's account information
  @throws HelloSignException thrown if there's a problem processing the
  HTTP request or the JSON response.