How to use Oauth2 for calling FCM V1 API

[vjayjz]

I want to call the FCM V1 messaging API, but as per V1 migration we need to take bearer token from the google Auth URL : https://accounts.google.com/o/oauth2/.  My idea for flow will be like we will call POST https://accounts.google.com/o/oauth2/  with client_id , Private_key and get token but currently we need to mention redirect_url as required parameter. How to get only token and not redirect and proceed to FCM API POST https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send.