title: Github Action: How to add secrets to application.properties file before build step
body: <p>I'm using Github Action CI/CD workflow to automate the build,test,deploy steps.In order to successfully build the project I need to include a secret variable (defined in the settings) to be written to application.properties file. However at the time of building  this variable is not found on the file. Here's workflow yml file</p>
  <pre><code>name: Build and deploy JAR app to Azure Web App - harry-kart-web-api
  
  on:
    push:
      branches:
        - master
    workflow_dispatch:
  
  jobs:
  
    compile:
      runs-on: windows-latest
      name: Running Java ${{ matrix.java }} compile
      steps:
      - uses: actions/checkout@v2
      - name: Set up Java version
        uses: actions/setup-java@v1
        with:
          java-version: '11'
      - name: Compile code
        run: mvn compile
  
  
  
    test:
      runs-on: windows-latest
      name: Running tests
      needs: compile
      steps:
        - uses: actions/checkout@v2
        - name: Set up Java version
          uses: actions/setup-java@v1
          with:
            java-version: '11'
        - name: Run unit tests
          run: mvn test
  
    build:
      runs-on: windows-latest
  
      steps:
      - uses: actions/checkout@v2
  
      - name: Set up Java version
        uses: actions/setup-java@v1
        with:
          java-version: '11'
  
      - name: Adding secret
        run: |
            echo $DEV_PROP_FILE &gt;&gt; src/main/resources/application.properties
            cat src/main/resources/application.properties
        shell: bash
        env:
          DEV_PROP_FILE: ${{secrets.AZURE_APPLICATION_INSIGHTS_INSTRUMENTATION_KEY}}
  
      - name: Build with Maven
        run: mvn clean install
  
      - name: Upload artifact for deployment job
        uses: actions/upload-artifact@v2
        with:
          name: java-app
          path: '${{ github.workspace }}/target/*.jar'
  
    deploy:
      runs-on: windows-latest
      needs: build
      environment:
        name: 'production'
        url: ${{ steps.deploy-to-webapp.outputs.webapp-url }}
  
      steps:
      - name: Download artifact from build job
        uses: actions/download-artifact@v2
        with:
          name: java-app
  
      - name: Deploy to Azure Web App
        id: deploy-to-webapp
        uses: azure/webapps-deploy@v2
        with:
          app-name: 'harry-kart-web-api'
          slot-name: 'production'
          publish-profile: ${{ secrets.AzureAppService_PublishProfile_c1d922ca006d4e828ca9710ff6d19933 }}
          package: '*.jar'
  </code></pre>