Integrate ALB with OIDC IdP:

In the AWS Management Console, navigate to the Application Load Balancer (ALB) settings.

Configure the ALB to use the OpenID Connect (OIDC) IdP for authentication. This ensures that all requests routed through the ALB are authenticated using the IdP.

Set Up Authentication Rules:

Create a listener rule on the ALB that requires authentication. This rule will forward requests to the IdP for user authentication before allowing access to the backend services.

Restrict Unauthenticated Access:

Ensure the ALB only forwards requests to backend services if the user is authenticated. Unauthenticated requests should be blocked or redirected to the IdP for authentication.

Update CloudFront Configuration:

Modify the CloudFront distribution to forward authenticated requests to the ALB. Ensure that the ALB and API Gateway accept only requests coming through the CloudFront distribution to enforce consistent authentication and security.

By enforcing authentication at the ALB level, you ensure that all backend services are accessed only by authenticated users, enhancing the overall security of the web application