로그인을 관장하는 AppController
https://ios-development.tistory.com/767
tabbar window hierarchy
https://stackoverflow.com/questions/21106888/attempt-to-present-viewcontroller-on-uitabbarcontroller-whose-view-is-not
dump로 자세한 내용 log출력
https://stackoverflow.com/questions/49806728/how-to-log-full-post-request-in-swift
2차전직 개발자가 되자