storePassword=<password from previous step>
keyPassword=<password from previous step>
keyAlias=upload
storeFile=C:/dev/keys/keystore.jks

def keystoreProperties = new Properties()
def keystorePropertiesFile = rootProject.file('key.properties')
if (keystorePropertiesFile.exists()) {
    keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
}

   signingConfigs {
       release {
           keyAlias keystoreProperties['keyAlias']
           keyPassword keystoreProperties['keyPassword']
           storeFile keystoreProperties['storeFile'] ? file(keystoreProperties['storeFile']) : null
           storePassword keystoreProperties['storePassword']
       }
   }
   buildTypes {
       release {
           signingConfig signingConfigs.release
       }
   }

PS C:\dev\workspace\flutter\puzzle_app> flutter build apk

 Building with sound null safety

Running Gradle task 'assembleRelease'...                           20.8s       
√  Built build\app\outputs\flutter-apk\app-release.apk (16.5MB).
PS C:\dev\workspace\flutter\puzzle_app>

プロジェクト レベルの build.gradle（<project>/build.gradle）:
####################
buildscript {
  repositories {
    // Check that you have the following line (if not, add it):
    google()  // Google's Maven repository

  }
  dependencies {
    ...
    // Add this line
    classpath 'com.google.gms:google-services:4.3.10'

  }
}

allprojects {
  ...
  repositories {
    // Check that you have the following line (if not, add it):
    google()  // Google's Maven repository

    ...
  }
}

apply plugin: 'com.android.application'

// Add this line
apply plugin: 'com.google.gms.google-services'


dependencies {
  // Import the Firebase BoM
  implementation platform('com.google.firebase:firebase-bom:30.0.0')


  // Add the dependency for the Firebase SDK for Google Analytics
  // When using the BoM, don't specify versions in Firebase dependencies
  implementation 'com.google.firebase:firebase-analytics'


  // Add the dependencies for any other desired Firebase products
  // https://firebase.google.com/docs/android/setup#available-libraries
}

# This is a basic workflow to help you get started with Actions

name: Flutter CI/CD

# Controls when the workflow will run
on:
  # Triggers the workflow on push or pull request events but only for the main branch
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]

  # Allows you to run this workflow manually from the Actions tab
  workflow_dispatch:

# A workflow run is made up of one or more jobs that can run sequentially or in parallel
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: subosito/flutter-action@v2
        with: 
          channel: 'stable'
      - run: flutter test
# This workflow contains a single job called "build"
  build:
    needs: test
    # The type of runner that the job will run on
    runs-on: ubuntu-latest

    # Steps represent a sequence of tasks that will be executed as part of the job
    steps:
      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
      - uses: actions/checkout@v3
      - uses: subosito/flutter-action@v2
        with:
          channel: 'stable'
      - uses: actions/setup-java@v1
        with:
          java-version: '11.x'
      - run: |
          KEYSTORE_PATH=$RUNNER_TEMP/keystore.jks
          echo -n $KEYSTORE | base64 --decode > $KEYSTORE_PATH
          
          KEY_PROPERTIES_PATH=android/key.properties
          echo "storePassword=$STORE_PASSWORD" >> $KEY_PROPERTIES_PATH
          echo "keyPassword=$KEY_PASSWORD"     >> $KEY_PROPERTIES_PATH
          echo "keyAlias=upload"               >> $KEY_PROPERTIES_PATH
          echo "storeFile=$KEYSTORE_PATH"      >> $KEY_PROPERTIES_PATH
        env:
          KEYSTORE: ${{ secrets.KEYSTORE }}
          STORE_PASSWORD: ${{ secrets.STORE_PASSWORD }}
          KEY_PASSWORD: ${{ secrets.KEY_PASSWORD }}
      - run: flutter build apk
      - uses: actions/upload-artifact@v3
        with:
          name: apk
          path: build/app/outputs/flutter-apk/app-release.apk

      # Runs a single command using the runners shell
      - name: Run a one-line script
        run: echo Hello, world!

      # Runs a set of commands using the runners shell
      - name: Run a multi-line script
        run: |
          echo Add other actions to build,
          echo test, and deploy your project.

      # Check test and build automatically
      - name: Check test and build automatically
        run: echo Automation!
  deploy:
    needs: build
    runs-on: ubuntu-latest
    steps:
      - uses: actions/download-artifact@v2
        with:
          name: apk
      - run: curl -sL https://firebase.tools | bash
      - run: firebase appdistribution:distribute app-release.apk --app $APP_ID --groups $TESTER_GROUP
        env: 
          FIREBASE_TOKEN: ${{ secrets.FIREBASE_TOKEN }}
          APP_ID: 1:YYYYYYYYYYYY:android:ZZZZZZZZZZZZZZZZZZZZZZ
          TESTER_GROUP: puzzle-app-group