Your company CSO (Chief Security Officer) has directed you to enhance the security of a critical application by implementing a CAPTCHA as part of the user sign-in process. What is the most efficient method to implement this capability?

Answer options:

A.Configure CAPTCHA Challenge in AWS Cognito User Pool.
B.Enable Amazon Pinpoint service.
C.Create a Pre Token Generation Lambda Trigger.
D.Create an Auth Challenge Lambda Trigger.

Answer: D
Option A is incorrect because AWS Cognito does not have this functionality.
Option B is incorrect because Amazon Pinpoint is a service for user analytics.
Option C is incorrect because Pre Token Generation Lambda Trigger is not an operation. That’s a part of the Custom Authentication Flow.
Option D is CORRECT because Create Auth Challenge is used as part of Custom authentication challenge triggers.
AWS Lambda functions can be created and then triggered during user pool operations such as user sign-up, confirmation, and sign-in (authentication) with a Lambda trigger to customize User Workflows.
The following table summarizes some of the customizations that can be made.
Custom authentication challenges can be implemented using Lambda triggers in Custom Authentication Flow shown below:
Reference:
Using Lambda Triggers:
https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-identity-pools-working-with-aws-lambda-triggers.html
Challenge Lambda Triggers:
https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-lambda-challenge.html