FCM 서버 구축

포스트맨에 구축하는 법
https://apoorv487.medium.com/testing-fcm-push-notification-through-postman-terminal-part-1-5c2df94e6c8d

파이썬에 구축하는 법
https://www.youtube.com/watch?v=P6DcYjOZ1XQ&ab_channel=%EB%82%98%EC%9D%B4%EC%8A%A4%EC%BD%94%EB%94%A9

firebase-admin-python
https://github.com/firebase/firebase-admin-python/blob/master/snippets/messaging/cloud_messaging.py

백그라운드에서 onMessaeReceived()가 호출되지 않는 원인 및 해결방법 (handleIntent)
https://medium.com/@jms8732/background%EC%97%90%EC%84%9C-onmessagereceived%EA%B0%80-%ED%98%B8%EC%B6%9C-%EC%95%88%EB%90%98%EB%8A%94-%ED%98%84%EC%83%81%EC%97%90-%EA%B4%80%ED%95%98%EC%97%AC-7595df624d91