title: Firebase function onCall, response: Warning, FIREBASE_CONFIG environment variable is missing. Initializing firebase-admin will fail
body: <p>I try to call my test function from local project.</p>
  
  <p>But all time when i call, i take 401 error. I don't know what trouble here, in front end i have init app with api key, in firebase function i have <code>admin.credential.applicationDefault()</code>;
  I tried to pass <code>admin.credential.cer(apiConfig)</code>, but this don't help to.</p>
  
  <p>I also have Environment variable <code>GOOGLE_APPLICATION_CREDENTIALS</code>, with path to my config.</p>
  
  <p><strong>Dependencies</strong></p>
  
  <pre><code>    "firebase-admin": "~7.0.0",
      "firebase-functions": "^2.2.0",
      "firebase-functions-test": "^0.1.6",
  </code></pre>
  
  <p><strong>My function</strong></p>
  
  <pre><code>import * as functions from 'firebase-functions';
  import * as admin from 'firebase-admin';
  
  admin.initializeApp({
      credential: admin.credential.applicationDefault(),
      databaseURL: "https://plan-list.firebaseio.com"
  });
  
  exports.createInviteUser = functions.https.onCall( (data, context)=&gt; {
  
    return data;
  
  });
  </code></pre>
  
  <p><strong>Front-end function request</strong></p>
  
  <pre><code> createInviteUser(email: string) {
          let inviteFunction = firebase.functions().httpsCallable('createInviteUser');
  
          inviteFunction(email)
              .then((result) =&gt; {
              // Read result of the Cloud Function.
             console.log(result);
          })
              .catch(err=&gt;{
                  console.log(err)
              });
      }
  </code></pre>
  
  <p>Also, how i see i have all required headers</p>
  
  <p><a href="https://i.stack.imgur.com/ArsrS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ArsrS.png" alt="enter image description here"></a>
  <strong>Here logs from console</strong></p>
  
  <pre><code>12:54:58.063 PM
  createInviteUser
  Warning, FIREBASE_CONFIG environment variable is missing. Initializing firebase-admin will fail
  12:55:36.257 PM
  createInviteUser
  Function execution started
  12:55:36.257 PM
  createInviteUser
   Billing account not configured. External network is not accessible and quotas are severely limited. Configure billing account to remove these restrictions
  12:55:36.271 PM
  createInviteUser
  Function execution took 15 ms, finished with status code: 204
  12:55:36.573 PM
  createInviteUser
  Function execution started
  12:55:36.573 PM
  createInviteUser
  Billing account not configured. External network is not accessible and quotas are severely limited. Configure billing account to remove these restrictions
  12:55:36.951 PM
  createInviteUser
  Function execution took 379 ms, finished with status code: 401
  </code></pre>