code: def add_user(
          self, user, first_name, last_name, email, password,
          url_prefix, auth, session, send_opts):
          
          req = self.get_user_request(
              'POST', 'application/json', url_prefix, auth,
              user, first_name, last_name, email, password)
  
          prep = session.prepare_request(req)
          resp = session.send(prep, **send_opts)
          if resp.status_code == 201:
              return
  
          msg = (
              'Failed adding user: {}, got HTTP response: ({}) - {}'
              .format(user, resp.status_code, resp.text))
          raise HTTPError(msg, request = req, response = resp)
docs: Add a new user.
  
          Args:
              user (string): User name.
              first_name (string): User's first name.
              last_name (string): User's last name.
              email: (string): User's email address.
              password: (string): User's password.
              url_prefix (string): Protocol + host such as https://api.theboss.io
              auth (string): Token to send in the request header.
              session (requests.Session): HTTP session to use for request.
              send_opts (dictionary): Additional arguments to pass to session.send().
  
          Raises:
              requests.HTTPError on failure.