I published a post this summer with a few simple demo applications I use when configuring AWS infrastructure. I needed something similar for a serverless application on AWS. In other words, a Lambda function sitting behind an API Gateway or Application Load Balancer (ALB).
I tend to use this simple Node.js function. It will return whatever it received as input. This is useful when you are debugging the infrastructure. For example, configuring Cognito with API Gateway or OIDC with ALB.