AWS Load Balancer Authentication with Cognito Testing

I'd like to use an Application Load Balancer (ALB) to authenticate requests with Cognito to my node express back-end. After authenticating, the ALB maintains session with a session cookie, and will forward a few headers to the back-end in form x-amzn-oidc-* (e.g. x-amzn-oidc-accesstoken).

So how do I develop and test token signature verification locally?