code: def client(self, client_name, **params):
          
          if client_name not in self.cfg.clients:
              raise OAuthException('Unconfigured client: %s' % client_name)
  
          if client_name not in ClientRegistry.clients:
              raise OAuthException('Unsupported services: %s' % client_name)
  
          params = dict(self.cfg.clients[client_name], **params)
          return ClientRegistry.clients[client_name](**params)
docs: Initialize OAuth client from registry.