api란? http://blog.wishket.com/api%EB%9E%80-%EC%89%BD%EA%B2%8C-%EC%84%A4%EB%AA%85-%EA%B7%B8%EB%A6%B0%ED%81%B4%EB%9D%BC%EC%9D%B4%EC%96%B8%ED%8A%B8/
Django user 관련 내용 https://han-py.tistory.com/353
custom user model 생성 방법 https://dev-yakuza.posstree.com/ko/django/custom-user-model/
한 app에서 다른 app의 key를 참조할 때 https://pythonq.com/so/python/43715