Customize federated sign-in with new Amazon Cognito Lambda trigger

This AWS blog post introduces the Amazon Cognito inbound federation Lambda trigger, describing how it intercepts external identity provider responses to transform, filter, and enrich user attributes before mapping them into a Cognito user pool. It includes two example use cases—filtering oversized SAML group attributes and automatic account linking across federated and local accounts—sample Lambda code for each, and operational best practices.