AWS Cognito: Unable to signup with custom attributes in UserPool

Question

I am trying to signup an user. I am using AWS cognito for user authentication and authorization. I have added new custom attribute "abc" in under attribute section in General Settings. I have enabled read & write for abc attribute in AppClients.

Now I am trying to hit the API to create user using Postman. I am able to create new user but problem I am facing is, I am unable to add custom attribute while creating user. To add custom attributes, everytime I have to run below cli command. How do I add custom attributes while creating user itself.

aws cognito-idp admin-update-user-attributes --user-pool-id us-west-2_aaaaaaaaa --username [email protected]  --user-attributes Name="custom:CustomAttr1",Value="Purple"

Answer 1

You can do the same by using the Post Confirmation Lambda Trigger, and writing relevant code in the Lambda trigger for this use-case.

Quoting the official AWS documentation for the Post Confirmation Lambda trigger:

Amazon Cognito invokes this trigger after a new user is confirmed, allowing you to send custom messages or to add custom logic.

Hence, this looks perfect for your use-case as you can call AdminUpdateUserAttributes from the Lambda code. From my experience, AWS Lambda operates the best and has the least cold start time when you write the code in Node.js or Python, so I would implore you to take a look at the recommended API calls.