title: Error on firebase admin nodejs Permission iam.serviceAccounts.signBlob is required
body: <p>im using this tutorial:
  <a href="https://firebase.google.com/docs/auth/admin/create-custom-tokens#using_a_service_account_id" rel="noreferrer">https://firebase.google.com/docs/auth/admin/create-custom-tokens#using_a_service_account_id</a></p>
  
  <p>to create a node.js function (deployed to google cloud functions) to authenticate my users. the function is super simple:</p>
  
  <pre><code>const admin = require('firebase-admin');
  admin.initializeApp({
     serviceAccountId: 'authenticator@igibo-b0b27.iam.gserviceaccount.com'
  });
  
  
  exports.authenticate = (req, res) =&gt; {
     let pass;
     let uid;
     if (req.query) {
        if (req.query.v == 3) {
           pass = req.query.p;
           uid = req.query.u;
        }
  
           admin.auth().createCustomToken(uid)
              .then(function(customToken) {
                 res.status(200).send(customToken);
                 return customToken;
              })
              .catch(function(error) {
                 console.error("Error creating custom token:" + JSON.stringify(error));
                 res.status(400).send(error);
              });
  
     } else {
        console.error("EMPTY to authentication");
        res.end();
     }
  };
  </code></pre>
  
  <p>but im getting this annoying error:</p>
  
  <pre><code>{"code":"auth/insufficient-permission","message":"Permission iam.serviceAccounts.signBlob is required to perform this operation on service account projects/-/serviceAccounts/authenticator@igibo-b0b27.iam.gserviceaccount.com.; Please refer to https://firebase.google.com/docs/auth/admin/create-custom-tokens for more details on how to use and troubleshoot this feature."}
  </code></pre>
  
  <p>in the very same tutorial it says i must go to IAM and adjust some roles for the service account WHICH I DID but still getting this error.</p>
  
  <p><a href="https://i.stack.imgur.com/hHaYp.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/hHaYp.jpg" alt=""></a></p>
  
  <p>this is a absolutelly simple task and shouldn't being such a hassle...
  what i am forgetting? the id is correct! the role is correct! the code is correct! </p>
  
  <p>what is wrong?</p>