hooks/useRegister.ts

(...)
import {applyToken} from '../api/client';

export default function useRegister() {
  const [, setUser] = useUserState();
  const navigation = useNavigation<RootStackNavigationProp>();
  const mutation = useMutation(register, {
    onSuccess: (data) => {
      setUser(data.user);
      navigation.pop();
      applyToken(data.jwt);
    },
    onError: (error: AuthError) => {
      console.log(error);
      /* TODO: 구현 예정 */
    },
  });
  return mutation;
}