title: Google Cloud API - Application Default Credentials
body: <p>I have the following code, modified from <a href="https://developers.google.com/identity/protocols/application-default-credentials" rel="noreferrer">Google's documentation</a>:</p>
  
  <pre><code>        $GOOGLE_APPLICATION_CREDENTIALS = "./[path].json";
          $_ENV["GOOGLE_APPLICATION_CREDENTIALS"] = "./[path].json";
          $_SERVER["GOOGLE_APPLICATION_CREDENTIALS"] = "./[path].json";
  
          $projectId = "[my project's ID']";
          $client = new Google_Client();
          $client-&gt;useApplicationDefaultCredentials();
          $client-&gt;setScopes(['https://www.googleapis.com/auth/books']);
          $service = new Google_Service_Books($client);
          $results = $service-&gt;volumes-&gt;listVolumes('Henry David Thoreau');
  </code></pre>
  
  <p>Yet when I run it it returns the error:</p>
  
  <pre><code>PHP Fatal error:  Uncaught exception 'DomainException' with message 'Could not load the default credentials. Browse to https://developers.google.com/accounts/docs/application-default-credentials for more information'
  </code></pre>
  
  <p>I have tried various configurations, for example changing the path of the file. As you see, I've also done the three different forms of variables that I could immediately think of (two environment, one not).</p>
  
  <p>I'm not quite sure where to look next. Should I look into different ways of setting the environment variable or should I define the path in a different way? What are the correct ways of doing this? Is there any other reason for the error?</p>