test.html

<button onclick="openWindow()">Open Auth Window</button>

<script>
function getBIToken(){
    let BIToken
    fetch('https://app.sandbox.datazip.io/api/v1/security/login', {
        method: 'POST',
        headers: {
            'Content-Type': 'application/json'
        },
        body: JSON.stringify({
            "password": "sandbox_8fbbff568d9fc0dc3def",
            "provider": "db",
            "refresh": true,
            "username": "sandbox_93bc63e0"
        })
        })
        .then(response => response.json())
        .then(data => {
        BIToken = data;
        console.log(`Received login token: ${loginToken}`);
        })
        .catch(error => {
        console.error(`Error during login: ${error}`);
        });
    return BIToken
}
getBIToken()
function openWindow() {
  
  const url = 'http://localhost:7070/api/oauth/airbyte-source-facebook-marketing/init?payload=';
  const name = 'authWindow';
  const features = 'height=600,width=800,resizable=yes';
  const authWindow = window.open(url, name, features);

  window.addEventListener('message', receiveMessage);

  function receiveMessage(event) {
    if (event.origin !== 'http://localhost:7070') {
      return;
    }

    if (event.data.type === 'auth_success') {
      const accessToken = event.data.accessToken;
      console.log(`Received access token: ${accessToken}`);
      authWindow.close();
      window.removeEventListener('message', receiveMessage);
    }
  }
}
</script>