docs: def client_factory(self):
          """
          Custom client factory to set proxy options.
          """
          
          if self._service.production:
              url = self.production_url
          else:
              url = self.testing_url
          
          proxy_options = dict()
          https_proxy_setting = os.environ.get('PAYEX_HTTPS_PROXY') or os.environ.get('https_proxy')
          http_proxy_setting = os.environ.get('PAYEX_HTTP_PROXY') or os.environ.get('http_proxy')
          
          if https_proxy_setting:
              proxy_options['https'] = https_proxy_setting
          if http_proxy_setting:
              proxy_options['http'] = http_proxy_setting
          
          return client.Client(url, proxy=proxy_options)