Cognito Identity returning the same ID every time - Node JS

I am trying to obtain a new Cognito Identity during the user signup process. Here's a code snippet:

aws.config.credentials = new aws.CognitoIdentityCredentials(unauthCred);
aws.config.credentials.get(function(err) {
    var id = aws.config.credentials.identityId;
}

I am expecting this to give me a new unique id every call. However, I am getting the same id every time. Is this the expected behavior? What can I do to get the behavior I want?