How do I set up an Application Load Balancer to authenticate users through an Amazon Cognito user pool without using Cognito hosted web UI?

I have followed the steps in this article: https://repost.aws/knowledge-center/cognito-user-pool-alb-authentication to set up ALB + Cognito authentication but it would end up triggering Cognito hosted web UI when I access the ALB url / the CName url.

How do I do it without Amazon Cognito hosted web UI? I would like to reuse the tokens that my users get from Cognito authentication process via Aws Amplify. My users should be already logged in via Aws Amplify before triggering this ALB + target group (lambda) endpoint.