Try finding a cognito user from a cognito identity, you can't.

Visit the amplify-js and amplify-cli github repos and search for cognito issues.

Try using the cognito console, it is a litter box of warning messages and exceptions. Try connecting Cognito and Pinpoint if you are in Europe, 2 years and it still doesn't work, but no indication.

See its cloudformation configuration and how many field changes cause a Replace. Yes, replace Cognito and goodbye users.

Until recently user names were case sensitive, and they didn't have basic account enumeration protections.

Its UX is exactly how DynamoDB can do damage to a product.

I recently built a new app on AWS and Lambda. I really wanted to use Cognito to keep everything in AWS. I fought with getting it working for a day or so before giving up and trying out Auth0. I was up and running with Auth0 in a couple hours. I found the Cognito documentation to be insufficient for my needs. Others may have better experiences.

Cognito has an awful API and worse documentation. It's also super limited in terms of how user metadata is represented, is hard to query efficiently for users meeting certain criteria, and produces super cryptic errors when integrations aren't set up correctly. As a whole the Cognito product feels like some weird bolted-on POC that AWS decided to charge money for. Compare that to a real _product_ like Auth0 and it just falls to pieces.

If the appeal is about free usage under 40k monthly active users, you probably don't need an external complex managed auth solution in the first place.