Thank you for the feedback.
I understand that Amazon Cognito could be a possible solution for this particular scenario.
On AWS there are multiple solutions that may accomplish the same outcome. Some solutions are preferable than others depending on the scenario.
On this particular question, we want to create complex scenario that involves RDS and Amazon S3 access with IAM permissions. We have other questions on our question bank that we have similar authentication scenario with Amazon Cognito. For this question, we want to provide some alternative solutions that previous answers.
Please note that this is a Professional level exam and we try to mimic AWS scenarios. Some of the questions do not explicitly show the obvious keywords or phrases that will easily point to the answer.
Hope this helps.
Let us know if you need further assistance. The Tutorials Dojo team is dedicated to helping you pass your AWS exam!
Kenneth Samonte @ Tutorials Dojo