As a Solutions Architect working for AWS, I had hands-on experience with Cognito when I chose it for my own company. It was a terrible decision - the code documentation of Cognito sucks, and my poor lead engineer spent many days trying to implement even basic functionality. We had it working in Prod for a few months.

He urged us to try Auth0, and was able to get everything working in a few hours. We've been using Auth0 happily for 18 months now. I recommend it.