Secured Cron Job for Google App Engine fails to start (Node js)

I am struggling with a cron job with secured URL in google app engine. As soon as I add login:admin in the app.yaml, the job fails to start (otherwise it works like a charm).

Here is my code:

• app.js

  const express = require('express');
  const app = express();
  
  app.get('/', (req, res) => {
    res.status(200).send('Hello, world!').end();
  });
  
  app.get('/admin', function(req, res){
   res.status(200).send('Hello, admin!').end();
  });
  
  
  // Start the server
  const PORT = process.env.PORT || 8080;
  app.listen(PORT, () => {
    console.log(`App listening on port ${PORT}`);
    console.log('Press Ctrl+C to quit.');
  });

• app.yaml

  runtime: nodejs
  env: flex
  
  handlers:
  - url: /
    script: app.js
    
  - url: /admin
    login: admin
    script: app.js

• cron.yaml

  cron:
  - description: daily summary job
    url: /admin
    schedule: every 12 mins
    target: default

And the result: cron failure

Any hint on what I am missing?

Thanks a lot in advance