I have created one user pool & identity pool.
I have used javascript sdk.
I am able to signup, send confirmation code & confirm user successfully with j
What you're trying to access here are "Cognito Federated Identity" credentials, which is a separate AWS product to "Cognito User Pools". In-order to retrieve these credentials, you need to connect your User Pool to your Federated Identity Pool.
Perhaps this link will help: http://docs.aws.amazon.com/cognito/latest/developerguide/amazon-cognito-integrating-user-pools-with-identity-pools.html
Also, I would remove admin access from Unauthenticated permissions, it means anyone with your details has control of your AWS account.