Is it possible to modify AWS Cognito user attributes in the Lambda triggers

Question

Having a look at the AWS documentation,

https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-identity-pools-working-with-aws-lambda-triggers.html#cogni

Answer 1

Well, the simple solution would be like so, adding this to the "Pre Sign-up Lambda function", taking cue from your code:

// Modify an existing username...
 event['request']['userAttributes']['name'] = "My_NAME";

// Add an additional attribute...
 event['request']['userAttributes']['custom:sillyname'] = "ANY_NAME";

 callback(null, event);

Considering you have added the custom:sillyname attribute for the user pool.