title: Use User-Defined build settings in custom .plist file
body: <p>I have different build configurations (Debug, Stage, Prod) defined for my app and I use <strong>User-Defined</strong> build settings:</p>
  
  <p><a href="https://i.stack.imgur.com/J4Gsj.png" rel="noreferrer"><img src="https://i.stack.imgur.com/J4Gsj.png" alt="enter image description here"></a></p>
  
  <p>to set up Facebook login and other stuff in <code>Info.plist</code> file: </p>
  
  <p><a href="https://i.stack.imgur.com/5nzFL.png" rel="noreferrer"><img src="https://i.stack.imgur.com/5nzFL.png" alt="enter image description here"></a></p>
  
  <p>In this scenario the <code>$(USER_DEFINED_SETTINGS)</code> notation <strong>does</strong> work. </p>
  
  <p>When I tried to set up <strong>Google SignIn</strong>, which requires using additional <code>.plist</code> file (<code>GoogleService-Info.plist</code>), and I used <strong>User-Defined</strong> settings in the same way I do in the <code>Info.plist</code> file, it doesn't work.</p>
  
  <p>How can I use <strong>User-Defined</strong> settings in custom <code>.plist</code> files? If I can't, how can I workaround this?</p>