I have created a lambda function and attached it as a pre and post login Trigger. I want this Lambda to triggered every time I am routed via AWS Cognito, not just logged in. Let me explain,

I have two App Clients:

App A -> Restricted

App B -> No Restrictions

User “john” tries to login to App A first. The Lambda trigger blocks him as it is a restricted group.

Lambda Code

const handler = async (event) => {
  if (
    event.userName === "john" && event.callerContext.clientId === "7hkgublahblah"
    // Block this user from using App A
  ) {
    throw new Error("This is a restricted Site.");
  }

  return event;
};

export { handler };

Faulty Sequence:

1. John goes to App B Logs in and comes back to App A,
2. App A Redirects John to Cognito,
3. Since he is already logged into Cognito (has a live session as he went to App B via Cognito)
4. He is allowed to access App A.
5. The Lambda is NOT Triggered this time

.

I want to write a functionality that will trigger a Lambda every time a user is redirected from Cognito to the App. So I can block certain users even if they have a Live Session with AWS Cognito i.e. are logged into Cognito by accessing some other App.