google/google-auth-library-rubyを利用したFCMへのプッシュ通知サンプル。Ruby on Rails前提

Gemfile

source 'https://rubygems.org'

gem 'rails'
# google/google-auth-library-ruby
gem 'googleauth'
# HTTPリクエストできればなんでもよい
gem 'faraday'

test_controller.rb

class TestController < ApplicationController
  def index
    scope = 'https://www.googleapis.com/auth/firebase.messaging'
    authorizer = Google::Auth::ServiceAccountCredentials.make_creds(json_key_io: nil, scope: scope)

    access_token = authorizer.fetch_access_token!

    # [your-project-name]にFirebaseプロジェクト名
    url = "https://fcm.googleapis.com/v1/projects/[your-project-name]/messages:send"

    request_body = {
        message: {
            # topic: "debug",
            condition: "'debug' in topics && 'news' in topics",
            notification: {
                title: "タイトル",
                body: "本文"
            },
            android: {
                priority: 'high'
            },
            apns: {
                headers: {
                    'apns-priority': '10'
                },
                payload: {
                    aps: {
                        sound: 'default'
                    }
                }
            }
        }
    }

    conn = Faraday.new(url: url)
    response = conn.post do |req|
      req.headers['Content-Type'] = 'application/json'
      req.headers['Authorization'] = "Bearer " + access_token["access_token"].to_s
      req.body = request_body.to_json
    end
    render :no_content
  end

end