How to get user attributes (username, email, etc.) using cognito identity id
I have AWS Cognito Identity Pool that is configured with Cognito User Pool as an authentication provider.
Assume I have identity ID of an identity in Cognito Identity Pool (e.g. us-east-1:XXaXcXXa-XXXX-XXXX-XXX-XXXXXXXXXXXX) where this identity has a linked login to a user in Cognito User Pool.
Using identity ID, how can I get the linked user details (email, phone, username)?
Answer
The ID Token that you exchange with Cognito federated identity service to get the identity id and credentials already has all user attributes. You do not need an extra call to any service.
It is a JWT token and you can use any library on the client to decode the values. You can read this guide for more information about the tokens vended by Cognito user pools.
Alternatively, you can also use the Access Token to call GetUser API which will return all the user information.