Which token is needed to send push notifications through POST - firebase

Question

I'm trying to set up a REST API server that could send push notifications using Firebase. Google documentation says this is a valid POST request, as a start :
POST https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1
Content-Type: application/json
Authorization: Bearer ya29.ElqKBGN2Ri_Uz...HnS_uNreA
{
"message":{
"topic" : "foo-bar",
"notification" : {
"body" : "This is a Firebase Cloud Messaging Topic Message!",
"title" : "FCM Message",
}
}
}
However, I can't figure out which Authorization bearer is expected here. There is a ton of them on the firebase console, and I've tried each and every one of them, none work. They all result in 401 response.
Where can I find the expected bearer for this request ?
Thanks !

Answer 1

I find it easier to use legacy protocols to send push notifications. We just need the Server key which can be found in the Firebase Console.
Firebase Console > Project Settings > Cloud Messaging > Server Key
HTTP request looks like this:
curl -X POST -H "Authorization: key=<your_server_key>" -H "Content-Type: application/json" -d '{
"notification": {
"body" : "This is a Firebase Cloud Messaging Topic Message!",
"title" : "FCM Message",
},
"to": "/topics/<topic_name>"
}' "https://fcm.googleapis.com/fcm/send"
Check Server Reference for other APIs for server implementation.

Answer 2

So, first of all go to Google Cloud Console and choose APIs&Services->Credentials. From there click on +Create Credentials->OAuth Client ID (Interface changes all the time so try to find this option). And then, simply choose Add Key and it will give you a json file.
After you receive your json file you can try what was given in this guide: https://firebase.google.com/docs/cloud-messaging/auth-server.
If you want to send request from Postman then you can try https://developers.google.com/oauthplayground. Register there with your google account and from available services select Firebase Cloud Messaging API v1 -> https://www.googleapis.com/auth/firebase.messaging. There in the second step press Exchange authorization code for tokens. Finally, you will get your Access and Refresh Token there